mẹo hay

Insert dữ liệu vào oracle lỗi utf-8 năm 2024

Oracle offers several database access products for inserting and retrieving Unicode data. Oracle offers database access products for commonly used programming environments such as Java and C/C++. Data is transparently converted between the database and client programs, which ensures that client programs are independent of the database character set and national character set. In addition, client programs are sometimes even independent of the character data type, such as

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 or

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4, used in the database.

To avoid overloading the database server with data conversion operations, Oracle always tries to move them to the client side database access products. In a few cases, data must be converted in the database, which affects performance. This chapter discusses details of the data conversion paths.

7.1.1 Database Access Product Stack and Unicode

Oracle offers a comprehensive set of database access products that enable programs from different development environments to access Unicode data stored in the database. These products are listed in the following table.

Table 7-1 Oracle Database Access Products

Programming Environment Oracle Database Access Products

C/C++

Oracle Call Interface [OCI]

Oracle Pro*C/C++

Oracle ODBC driver

Oracle Provider for OLE DB

Oracle Data Provider for .NET

Java

Oracle JDBC OCI or thin driver

Oracle server-side thin driver

Oracle server-side internal driver

PL/SQL

Oracle PL/SQL and SQL

Visual Basic/C#

Oracle ODBC driver

Oracle Provider for OLE DB

The following figure shows how the database access products can access the database.

The Oracle Call Interface [OCI] is the lowest level API that the rest of the client-side database access products use. It provides a flexible way for C/C++ programs to access Unicode data stored in SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types. Using OCI, you can programmatically specify the character set [UTF-8, UTF-16, and others] for the data to be inserted or retrieved. It accesses the database through Oracle Net.

Oracle Pro*C/C++ enables you to embed SQL and PL/SQL in your programs. It uses OCI's Unicode capabilities to provide UTF-16 and UTF-8 data access for SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types.

The Oracle ODBC driver enables C/C++, Visual Basic, and VBScript programs running on Windows platforms to access Unicode data stored in SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types of the database. It provides UTF-16 data access by implementing the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

1 interface specified in the ODBC standard specification.

The Oracle Provider for OLE DB enables C/C++, Visual Basic, and VBScript programs running on Windows platforms to access Unicode data stored in SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types. It provides UTF-16 data access through wide string OLE DB data types.

The Oracle Data Provider for .NET enables programs running in any .NET programming environment on Windows platforms to access Unicode data stored in SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types. It provides UTF-16 data access through Unicode data types.

Oracle JDBC drivers are the primary Java programmatic interface for accessing an Oracle database. Oracle provides the following JDBC drivers:

The JDBC OCI driver that is used by Java applications and requires the OCI library
The JDBC thin driver, which is a pure Java driver that is primarily used by Java applets and supports the Oracle Net protocol over TCP/IP
The JDBC server-side thin driver, a pure Java driver used inside Java stored procedures to connect to another Oracle server
The JDBC server-side internal driver that is used inside the Oracle server to access the data in the database

All drivers support Unicode data access to SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types in the database.

The PL/SQL and SQL engines process PL/SQL programs and SQL statements on behalf of client-side programs such as OCI and server-side PL/SQL stored procedures. They allow PL/SQL programs to declare

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3, and

NAME

John Smith

1 variables and to access SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types in the database.

The following sections describe how each of the database access products supports Unicode data access to an Oracle database and offer examples for using those products:

7.2 SQL and PL/SQL Programming with Unicode

7.2.1 SQL NCHAR Data Types

7.2.1.1 The NCHAR Data Type

When you define a table column or a PL/SQL variable as the

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data type, the length is always specified as the number of characters. For example, the following statement creates a column with a maximum length of 30 characters:

CREATE TABLE table1 [column1 NCHAR[30]];

The maximum number of bytes for the column is determined as follows:

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

For example, if the national character set is UTF8, then the maximum byte length is 30 characters times 3 bytes for each character, or 90 bytes.

The national character set, which is used for all

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types, is defined when the database is created. The national character set can be either UTF8 or AL16UTF16. The default is AL16UTF16.

The maximum column size allowed is 32000 characters when the national character set is UTF8 and 8000 when it is AL16UTF16. The actual data is subject to the maximum byte limit of 16000. The two size constraints must be satisfied at the same time. In PL/SQL, the maximum length of

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data is 32767 bytes. You can define an

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 variable of up to 32767 characters, but the actual data cannot exceed 32767 bytes. If you insert a value that is shorter than the column length, then Oracle pads the value with blanks to whichever length is smaller: maximum character length or maximum byte length.

Note:

UTF8 may affect performance because it is a variable-width character set. Excessive blank padding of

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 fields decreases performance. Consider using the

NAME

John Smith

1 data type or changing to the AL16UTF16 character set for the

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data type.

7.2.1.2 The NVARCHAR2 Data Type

The

NAME

John Smith

1 data type specifies a variable length character string that uses the national character set. When you create a table with an

NAME

John Smith

1 column, you specify the maximum number of characters for the column. Lengths for

NAME

John Smith

1 are always in units of characters, just as for

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3. Oracle subsequently stores each value in the column exactly as you specify it, if the value does not exceed the column's maximum length. Oracle does not pad the string value to the maximum length.

The maximum length for the

NAME

John Smith

1 type is 4000 characters if

DECLARE ndatestring NVARCHAR2[20] := N'12-SEP-1975'; ndstr NVARCHAR2[50]; BEGIN SELECT name INTO ndstr FROM customers WHERE [birthdate]> TO_DATE[ndatestring, 'DD-MON-YYYY', NLS_DATE_LANGUAGE = 'AMERICAN']; END;

8 or 32767 characters if

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

1. These lengths are based on using UTF8; the values are 2000 and 16383 characters when using AL16UTF16.

In PL/SQL, the maximum length for an

NAME

John Smith

1 variable is 32767 bytes. You can define

NAME

John Smith

1 variables up to 32767 characters, but the actual data cannot exceed 32767 bytes.

The following statement creates a table with one

NAME

John Smith

1 column whose maximum length in characters is 2000 and maximum length in bytes is 4000.

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

7.2.1.3 The NCLOB Data Type

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

5 is a character large object containing Unicode characters, with a maximum size of 4 gigabytes. Unlike the

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

6 data type, the

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

5 data type has full transactional support so that changes made through SQL, the

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

8 package, or OCI participate fully in transactions. Manipulations of

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

5 value can be committed and rolled back. Note, however, that you cannot save an

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

5 locator in a PL/SQL or OCI variable in one transaction and then use it in another transaction or session.

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

5 values are stored in the database in a format that is compatible with UCS-2, regardless of the national character set. Oracle translates the stored Unicode value to the character set requested on the client or on the server, which can be fixed-width or variable-width. When you insert data into an

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

5 column using a variable-width character set, Oracle converts the data into a format that is compatible with UCS-2 before storing it in the database.

7.2.2 Implicit Data Type Conversion Between NCHAR and Other Data Types

Oracle supports implicit conversions between SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types and other Oracle data types, such as

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

SELECT CONCAT[name,id] FROM customers;

8, and

SELECT CONCAT[name,id] FROM customers;

9. Any implicit conversions for

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

9 data types are also supported for SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types. You can use SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types the same way as SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types.

Type conversions between SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types and SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types may involve character set conversion when the database and national character sets are different. Padding with blanks may occur if the target data is either

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 or

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

7.2.3 Exception Handling for Data Loss During Data Type Conversion

Data loss can occur during data type conversion when character set conversion is necessary. If a character in the source character set is not defined in the target character set, then a replacement character is used in its place. For example, if you try to insert

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data into a regular

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 column and the character data in

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 [Unicode] form cannot be converted to the database character set, then the character is replaced by a replacement character defined by the database character set. The

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

12 initialization parameter controls the behavior of data loss during character type conversion. When this parameter is set to

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

13, any SQL statements that result in data loss return an

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

14 error and the corresponding operation is stopped. When this parameter is set to

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

15, data loss is not reported and the unconvertible characters are replaced with replacement characters. The default value is

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

15. This parameter works for both implicit and explicit conversion.

In PL/SQL, when data loss occurs during conversion of SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types, the

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

19 exception is raised for both implicit and explicit conversion.

7.2.4 Rules for Implicit Data Type Conversion

In some cases, conversion between data types is possible in only one direction. In other cases, conversion in both directions is possible. Oracle defines a set of rules for conversion between data types. The following table contains the rules for conversion between data types.

Table 7-2 Rules for Conversion Between Data Types

Statement Rule

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

20/

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

21 statement

Values are converted to the data type of the target database column.

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

23 statement

Data from the database is converted to the data type of the target variable.

Variable assignments

Values on the right of the equal sign are converted to the data type of the target variable on the left of the equal sign.

Parameters in SQL and PL/SQL functions

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3, and

NAME

John Smith

1 are loaded the same way. An argument with a

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 or

NAME

John Smith

1 data type is compared to a formal parameter of any of the

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 or

NAME

John Smith

1 data types. If the argument and formal parameter data types do not match exactly, then implicit conversions are introduced when data is copied into the parameter on function entry and copied out to the argument on function exit.

Concatenation || operation or

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

36 function

If one operand is a SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 or

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data type and the other operand is a

SELECT CONCAT[name,id] FROM customers;

6 or other non-character data type, then the other data type is converted to

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

9 or

NAME

John Smith

1. For concatenation between character data types, see "".

SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 or

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types and

SELECT CONCAT[name,id] FROM customers;

6 data type

Character values are converted to

SELECT CONCAT[name,id] FROM customers;

6 data type.

SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 or

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types and

SELECT CONCAT[name,id] FROM customers;

7 data type

Character values are converted to

SELECT CONCAT[name,id] FROM customers;

7 data type.

SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 or

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types and

SELECT CONCAT[name,id] FROM customers;

8 data type

Character values are converted to

SELECT CONCAT[name,id] FROM customers;

8 data type.

SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types and SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types

Comparisons between SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types and SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types are more complex because they can be encoded in different character sets.

When

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

9 values are compared, the

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 values are converted to

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

9 values.

When

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 and

NAME

John Smith

1 values are compared, the

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 values are converted to

NAME

John Smith

1 values.

When there is comparison between SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types and SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types, character set conversion occurs if they are encoded in different character sets. The character set for SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types is always Unicode and can be either UTF8 or AL16UTF16 encoding, which have the same character repertoires but are different encodings of the Unicode standard. SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types use the database character set, which can be any character set that Oracle supports. Unicode is a superset of any character set supported by Oracle, so SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types can always be converted to SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types without data loss.

7.2.5 SQL Functions for Unicode Data Types

SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types can be converted to and from SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types and other data types using explicit conversion functions. The examples in this section use the table created by the following statement:

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

Example 7-1 Populating the Customers Table Using the TO_NCHAR Function

The

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

74 function converts the data at run time, while the

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

75 function converts the data at compilation time.

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

Example 7-2 Selecting from the Customer Table Using the TO_CHAR Function

The following statement converts the values of

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

76 from characters in the national character set to characters in the database character set before selecting them according to the

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

77 clause:

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

You should see the following output:

NAME

John Smith

Example 7-3 Selecting from the Customer Table Using the TO_DATE Function

Using the

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

75 function shows that either

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 or

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data can be passed as parameters for the

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

81 function. The data types can mixed because they are converted at run time.

As demonstrated in , SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data can be passed to explicit conversion functions. SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data can be mixed together when using multiple string parameters.

7.2.6 Other SQL Functions

Most SQL functions can take arguments of SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types as well as mixed character data types. The return data type is based on the type of the first argument. If a non-string data type like

SELECT CONCAT[name,id] FROM customers;

6 or

SELECT CONCAT[name,id] FROM customers;

7 is passed to these functions, then it is converted to

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

9. The following examples use the

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

89 table created in "".

Example 7-4 INSTR Function

In this example, the string literal

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

90 is converted to

NAME

John Smith

1 and then scanned by

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

92, to detect the position of the first occurrence of this string in

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

76.

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

Example 7-5 CONCAT Function

SELECT CONCAT[name,id] FROM customers;

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

94 is converted to

NAME

John Smith

1 and then concatenated with

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

76.

Example 7-6 RPAD Function

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

The following output results:

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

The space character ' ' is converted to the corresponding character in the

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 character set and then padded to the right of

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

76 until the total display length reaches 100.

7.2.7 Unicode String Literals

You can input Unicode string literals in SQL and PL/SQL as follows:

Put a prefix maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character] 75 before a string literal that is enclosed with single quotation marks. This explicitly indicates that the following string literal is an INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3 string literal. For example, CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 01 is an INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3 string literal. For information about limitations of this method, see "".
Use the
CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 03 CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 04 CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 05 SQL function, which returns a unit of character code in the national character set, which is AL16UTF16 or UTF8. The result of concatenating several CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 03 CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 04 CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 05 functions is NAME
John Smith 1 data. In this way, you can bypass the client and server character set conversions and create an NAME
John Smith 1 string directly. For example, CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 11 represents a blank character. Because CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 03 CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 04 CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 05 is associated with the national character set, portability of the resulting value is limited to applications that run with the same national character set. If this is a concern, then use the CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 15 function to remove portability limitations.
Use the CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 15[' CREATE TABLE table2 [column2 NVARCHAR2[2000]];
SQL function. CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 15[' CREATE TABLE table2 [column2 NVARCHAR2[2000]];
converts a string to the national character set. To ensure portability and to preserve data, include only ASCII characters and Unicode encoding in the following form: CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 20, where CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 21 is the hexadecimal value of a character code value in UTF-16 encoding format. For example, CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 22 represents CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 23. The ASCII characters are converted to the database character set and then to the national character set. The Unicode encoding is converted directly to the national character set.

The last two methods can be used to encode any Unicode string literals.

7.2.8 NCHAR String Literal Replacement

This section provides information on how to avoid data loss when performing

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 string literal replacement.

Being part of a SQL or PL/SQL statement, the text of any literal, with or without the prefix

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

75, is encoded in the same character set as the rest of the statement. On the client side, the statement is in the client character set, which is determined by the client character set defined in

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26, or specified in the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

27 call, or predefined as UTF-16 in JDBC. On the server side, the statement is in the database character set.

When the SQL or PL/SQL statement is transferred from client to the database server, its character set is converted accordingly. It is important to note that if the database character set does not contain all characters used in the text literals, then the data is lost in this conversion. This problem affects INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3 string literals more than the INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 4 text literals. This is because the CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 30 literals are designed to be independent of the database character set, and should be able to provide any data that the client character set supports. To avoid data loss in conversion to an incompatible database character set, you can activate the INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3 literal replacement functionality. The functionality transparently replaces the CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 30 literals on the client side with an internal format. The database server then decodes this to Unicode when the statement is executed.
The sections "" and "" show how to switch on the replacement functionality in OCI and JDBC, respectively. Because many applications, for example, SQL*Plus, use OCI to connect to a database, and they do not control INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3 literal replacement explicitly, you can set the client environment variable CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 34 to maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character] 13 to control the functionality for them. By default, the functionality is switched off to maintain backward compatibility.

7.2.9 Using the UTL_FILE Package with NCHAR Data

The

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

36 package handles Unicode national character set data of the

NAME

John Smith

1 data type.

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 and

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

5 are supported through implicit conversion. The functions and procedures include the following:

CREATE TABLE table2 [column2 NVARCHAR2[2000]];
40 This function opens a file in national character set mode for input or output, with the maximum line size specified. Even though the contents of an NAME
John Smith 1 buffer may be AL16UTF16 or UTF8 [depending on the national character set of the database], the contents of the file are always read and written in UTF8. See "" for more information. CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 36 converts between UTF8 and AL16UTF16 as necessary.
CREATE TABLE table2 [column2 NVARCHAR2[2000]];
43 This procedure reads text from the open file identified by the file handle and places the text in the output buffer parameter. The file must be opened in national character set mode, and must be encoded in the UTF8 character set. The expected buffer data type is NAME
John Smith 1. If a variable of another data type, such as INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3, SELECT INSTR[name, N'Sm', 1, 1] FROM customers; 5, or SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 9 is specified, PL/SQL performs standard implicit conversion from NAME
John Smith 1 after the text is read.
CREATE TABLE table2 [column2 NVARCHAR2[2000]];
49 This procedure writes the text string stored in the buffer parameter to the open file identified by the file handle. The file must be opened in the national character set mode. The text string will be written in the UTF8 character set. The expected buffer data type is NAME
John Smith 1. If a variable of another data type is specified, PL/SQL performs implicit conversion to NAME
John Smith 1 before writing the text.
CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 52 This procedure is equivalent to CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 49, except that the line separator is appended to the written text.
CREATE TABLE table2 [column2 NVARCHAR2[2000]];
54 This procedure is a formatted version of a CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 49 procedure. It accepts a format string with formatting elements \n and %s, and up to five arguments to be substituted for consecutive instances of %s in the format string. The expected data type of the format string and the arguments is NAME
John Smith 1. If variables of another data type are specified, PL/SQL performs implicit conversion to NAME
John Smith 1 before formatting the text. Formatted text is written in the UTF8 character set to the file identified by the file handle. The file must be opened in the national character set mode.

The above functions and procedures process text files encoded in the UTF8 character set, that is, in the Unicode CESU-8 encoding. See "" for more information about CESU-8. The functions and procedures convert between UTF8 and the national character set of the database, which can be UTF8 or AL16UTF16, as needed.

7.3 OCI Programming with Unicode

7.3.1 OCIEnvNlsCreate[] Function for Unicode Programming

The

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

27 function is used to specify a SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 character set and a SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 character set when the OCI environment is created. It is an enhanced version of the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

61 function and has extended arguments for two character set IDs. The OCI_UTF16ID UTF-16 character set ID replaces the Unicode mode introduced in Oracle9i release 1 [9.0.1]. For example:

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

The Unicode mode, in which the OCI_UTF16 flag is used with the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

61 function, is deprecated.

When OCI_UTF16ID is specified for both SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 character sets, all metadata and bound and defined data are encoded in UTF-16. Metadata includes SQL statements, user names, error messages, and column names. Thus, all inherited operations are independent of the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 setting, and all metatext data parameters [

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

are assumed to be Unicode text data types [

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

in UTF-16 encoding.

To prepare the SQL statement when the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

68 function is initialized with the OCI_UTF16ID character set ID, call the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

69 function with a

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

70 string. The following example runs on the Windows platform only. You may need to change

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

71 data types for other platforms.

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

To bind and define data, you do not have to set the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

72 attribute because the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

68 function has already been initialized with UTF-16 character set IDs. The bind variable names also must be UTF-16 strings.

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

The

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

74 function performs the operation.

7.3.2 OCI Unicode Code Conversion

Unicode character set conversions take place between an OCI client and the database server if the client and server character sets are different. The conversion occurs on either the client or the server depending on the circumstances, but usually on the client side.

7.3.2.1 Data Integrity

You can lose data during conversion if you call an OCI API inappropriately. If the server and client character sets are different, then you can lose data when the destination character set is a smaller set than the source character set. You can avoid this potential problem if both character sets are Unicode character sets [for example, UTF8 and AL16UTF16].

When you bind or define SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types, you should set the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

76 attribute to

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

77. Otherwise, you can lose data because the data is converted to the database character set before converting to or from the national character set. This occurs only if the database character set is not Unicode.

7.3.2.2 OCI Performance Implications When Using Unicode

Redundant data conversions can cause performance degradation in your OCI applications. These conversions occur in two cases:

When you bind or define SQL INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 4 data types and set the CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 76 attribute to CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 77, data conversions take place from client character set to the national database character set, and from the national character set to the database character set. No data loss is expected, but two conversions happen, even though it requires only one.
When you bind or define SQL INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3 data types and do not set CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 76, data conversions take place from client character set to the database character set, and from the database character set to the national database character set. In the worst case, data loss can occur if the database character set is smaller than the client's.

To avoid performance problems, you should always set

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

76 correctly, based on the data type of the target columns. If you do not know the target data type, then you should set the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

76 attribute to

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

77 when binding and defining.

The following table contains information about OCI character set conversions.

Table 7-3 OCI Character Set Conversions

Data Types for OCI Client Buffer OCI_ATTR_CHARSET_FORM Data Types of the Target Column in the Database Conversion Between Comments

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

SELECT CONCAT[name,id] FROM customers;

UTF-16 and database character set in OCI

No unexpected data loss

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

UTF-16 and national character set in OCI

No unexpected data loss

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

SELECT CONCAT[name,id] FROM customers;

UTF-16 and national character set in OCI

National character set and database character set in database server

No unexpected data loss, but may degrade performance because the conversion goes through the national character set

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

UTF-16 and database character set in OCI

Database character set and national character set in database server

Data loss may occur if the database character set is not Unicode

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

SELECT CONCAT[name,id] FROM customers;

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set and database character set in OCI

No unexpected data loss

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set and national character set in OCI

No unexpected data loss

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

SELECT CONCAT[name,id] FROM customers;

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set and national character set in OCI

National character set and database character set in database server

No unexpected data loss, but may degrade performance because the conversion goes through the national character set

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set and database character set in OCI

Database character set and national character set in database server

Data loss may occur because the conversion goes through the database character set

7.3.2.3 OCI Unicode Data Expansion

Data conversion can result in data expansion, which can cause a buffer to overflow. For binding operations, you must set the

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

22 attribute to a large enough size to hold the expanded data on the server. If this is difficult to do, then you must consider changing the table schema. For defining operations, client applications must allocate enough buffer space for the expanded data. The size of the buffer should be the maximum length of the expanded data. You can estimate the maximum buffer length with the following calculation:

Get the column data byte size.
Multiply it by the maximum number of bytes for each character in the client character set.

This method is the simplest and quickest way, but it may not be accurate and can waste memory. It is applicable to any character set combination. For example, for UTF-16 data binding and defining, the following example calculates the client buffer:

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

7.3.3 Setting UTF-8 to the NLS_LANG Character Set in OCI

For OCI client applications that support Unicode UTF-8 encoding, use AL32UTF8 to specify the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set, unless the database character set is UTF8. Use UTF8 if the database character set is UTF8.

Do not set

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 to AL16UTF16, because AL16UTF16 is the national character set for the server. If you need to use UTF-16, then you should specify the client character set to

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

25, using the

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

26 function when binding or defining data.

7.3.4 Binding and Defining SQL CHAR Data Types in OCI

To specify a Unicode character set for binding and defining data with SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types, you may need to call the

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

26 function to set the appropriate character set ID after

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

29 or

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

30 APIs. There are two typical cases:

Call CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 29 or CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 30 followed by CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 33[] to specify UTF-16 Unicode character set encoding. For example: maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character] 6 If bound buffers are of the CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 86 data type, then you should add a cast [ CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 02*] when CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 29 or CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 30 is called. The value of the CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 22 attribute is usually determined by the column size of the server character set because this size is only used to allocate temporary buffer space for conversion on the server when you perform binding operations.
Call CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 29 or CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 30 with the CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 26 character set specified as UTF8 or AL32UTF8. UTF8 or AL32UTF8 can be set in the CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 26 environment variable. You call CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 29 and CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 30 in exactly the same manner as when you are not using Unicode. Set the CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 26 environment variable to UTF8 or AL32UTF8 and run the following OCI program: maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character] 7

7.3.5 Binding and Defining SQL NCHAR Data Types in OCI

Oracle recommends that you access SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types using UTF-16 binding or defining when using OCI. Beginning with Oracle9i, SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types are Unicode data types with an encoding of either UTF8 or AL16UTF16. To access data in SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types, set the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

76 attribute to

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

77 between binding or defining and execution so that it performs an appropriate data conversion without data loss. The length of data in SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types is always in the number of Unicode code units.

The following program is a typical example of inserting and fetching data against an

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data column:

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

7.3.6 Handling SQL NCHAR String Literals in OCI

By default, the

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 literal replacement is not enabled in OCI. You can enable it in OCI by setting the environment variable

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

34 to

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

13.

You can also enable literal replacement programmatically in OCI by using the

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

56 and

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

57 modes in

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

61 and

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

27. For example,

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

60 enables

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 literal replacement and

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

62 disables it.

As an example, consider the following statement:

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

Note:

When

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 literal replacement is enabled,

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

64 and

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

65 transform

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

30 literals with

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

67 literals in the SQL text and store the resulting SQL text in the statement handle. Thus, if an application uses

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

68 to retrieve the SQL text from the OCI statement handle, the SQL text returns

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

67 instead of

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

30 as specified in the original text.

7.3.7 Binding and Defining CLOB and NCLOB Unicode Data in OCI

In order to write [bind] and read [define] UTF-16 data for

SELECT CONCAT[name,id] FROM customers;

9 or

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

5 columns, the UTF-16 character set ID must be specified as

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

73 and

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

74. When you write UTF-16 data into a

SELECT CONCAT[name,id] FROM customers;

9 column, call

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

73 as follows:

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

The

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

77 parameter is the data length in number of Unicode code units. The

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

78 parameter indicates the offset of data from the beginning of the data column. The

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

79 parameter must be set for UTF-16 data.

To read UTF-16 data from

SELECT CONCAT[name,id] FROM customers;

9 columns, call

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

74 as follows:

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

The data length is always represented in the number of Unicode code units. Note one Unicode supplementary character is counted as two code units, because the encoding is UTF-16. After binding or defining a

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

82 column, you can measure the data length stored in the

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

82 column using

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

84. The returning value is the data length in the number of code units if you bind or define as UTF-16.

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

If you are using an

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

5, then you must set

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

76 to

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

77.

7.4 Pro*C/C++ Programming with Unicode

Pro*C/C++ provides the following ways to insert or retrieve Unicode data into or from the database:

Using the CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 88 Pro*C/C++ data type or the native C/C++ CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 02 data type, a program can access Unicode data stored in SQL INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 4 data types of a UTF8 or AL32UTF8 database. Alternatively, a program could use the C/C++ native CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 02 type.
Using the CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 92 Pro*C/C++ data type or the native C/C++ CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 86 data type, a program can access Unicode data stored in INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3 data types of a database.
Using the CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 95 Pro*C/C++ data type, a program can access Unicode data stored in INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3 data types. The difference between CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 92 and CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 95 in a Pro*C/C++ program is that the data for the CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 92 data type is stored in a CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 86 buffer while the data for the CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 95 data type is stored in a CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 02 data type.

Pro*C/C++ does not use the Unicode OCI API for SQL text. As a result, embedded SQL text must be encoded in the character set specified in the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 environment variable.

This section contains the following topics:

7.4.1 Pro*C/C++ Data Conversion in Unicode

Data conversion occurs in the OCI layer, but it is the Pro*C/C++ preprocessor that instructs OCI which conversion path should be taken based on the data types used in a Pro*C/C++ program. The following table shows the conversion paths.

Table 7-4 Pro*C/C++ Bind and Define Data Conversion

Pro*C/C++ Data Type SQL Data Type Conversion Path

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

88 or

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set to and from the database character set happens in OCI

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

88 or

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set to and from database character set happens in OCI

Database character set to and from national character set happens in database server

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set to and from national character set happens in OCI

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set to and from national character set happens in OCI

National character set to and from database character set in database server

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

92 or

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

UTF-16 to and from the national character set happens in OCI

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

92 or

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

UTF-16 to and from national character set happens in OCI

National character set to database character set happens in database server

7.4.2 Using the VARCHAR Data Type in Pro*C/C++

The Pro*C/C++

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

88 data type is preprocessed to a struct with a

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

25 field and

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

02 buffer field. The following example uses the C/C++

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

02 native data type and the

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

88 Pro*C/C++ data types to bind and define table columns.

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

When you use the

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

88 data type or native

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

02 data type in a Pro*C/C++ program, the preprocessor assumes that the program intends to access columns of SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types instead of SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types in the database. The preprocessor generates C/C++ code to reflect this fact by doing a bind or define using the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

87 value for the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

76 attribute. As a result, if a bind or define variable is bound to a column of SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types in the database, then implicit conversion occurs in the database server to convert the data from the database character set to the national database character set and vice versa. During the conversion, data loss occurs when the database character set is a smaller set than the national character set.

7.4.3 Using the NVARCHAR Data Type in Pro*C/C++

The Pro*C/C++

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

95 data type is similar to the Pro*C/C++

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

88 data type. It should be used to access SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types in the database. It tells Pro*C/C++ preprocessor to bind or define a text buffer to the column of SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types. The preprocessor specifies the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

77 value for the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

76 attribute of the bind or define variable. As a result, no implicit conversion occurs in the database.

If the

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

95 buffer is bound against columns of SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types, then the data in the

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

95 buffer [encoded in the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set] is converted to or from the national character set in OCI, and the data is then converted to the database character set in the database server. Data can be lost when the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set is a larger set than the database character set.

7.4.4 Using the UVARCHAR Data Type in Pro*C/C++

The

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

92 data type is preprocessed to a struct with a

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

25 field and

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

86 buffer field. The following example code contains two host variables,

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

50 and

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

51. The

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

50 host variable is declared as a

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

86 buffer containing 20 Unicode characters. The

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

51 host variable is declared as a

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

55 buffer containing 50 Unicode characters. The

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

56 and

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

57 fields are accessible as fields of a struct.

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

When you use the

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

92 data type or native

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

86 data type in Pro*C/C++ programs, the preprocessor assumes that the program intends to access SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types. The preprocessor generates C/C++ code by binding or defining using the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

77 value for

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

76 attribute. As a result, if a bind or define variable is bound to a column of a SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data type, then an implicit conversion of the data from the national character set occurs in the database server. However, there is no data lost in this scenario because the national character set is always a larger set than the database character set.

7.5 JDBC Programming with Unicode

7.5.1 Binding and Defining Java Strings to SQL CHAR Data Types

Oracle JDBC drivers allow you to access SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types in the database using Java string bind or define variables. The following code illustrates how to bind a Java string to a

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 column.

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

You can define the target SQL columns by specifying their data types and lengths. When you define a SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 column with the data type and the length, JDBC uses this information to optimize the performance of fetching SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data from the column. The following is an example of defining a SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 column.

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

You must cast

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

69 to

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

70 to call

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

71. The second parameter of

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

71 is the data type of the target SQL column. The third parameter is the length in number of characters.

7.5.2 Binding and Defining Java Strings to SQL NCHAR Data Types

For binding or defining Java string variables to SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types, Oracle provides an extended

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

69 which has the

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

75 method through which you can explicitly specify the target column of a bind variable to be a SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data type. The following code illustrates how to bind a Java string to an

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 column.

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

You can define the target SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 columns by specifying their data types, forms of use, and lengths. JDBC uses this information to optimize the performance of fetching SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data from these columns. The following is an example of defining a SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 column.

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

To define a SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 column, you must specify the data type that is equivalent to a SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 column in the first argument, the length in number of characters in the second argument, and the form of use in the fourth argument of

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

71.

You can bind or define a Java string against an

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 column without explicitly specifying the form of use argument. This implies the following:

If you do not specify the argument in the INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 85 method, then JDBC assumes that the bind or define variable is for the SQL INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 4 column. As a result, it tries to convert them to the database character set. When the data gets to the database, the database implicitly converts the data in the database character set to the national character set. During this conversion, data can be lost when the database character set is a subset of the national character set. Because the national character set is either UTF8 or AL16UTF16, data loss would happen if the database character set is not UTF8 or AL32UTF8.
Because implicit conversion from SQL INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 4 to SQL INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3 data types happens in the database, database performance is degraded.

In addition, if you bind or define a Java string for a column of SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 data types but specify the form of use argument, then performance of the database is degraded. However, data should not be lost because the national character set is always a larger set than the database character set.

7.5.2.1 New JDBC4.0 Methods for NCHAR Data Types

JDBC 11.1 adds support for the new JDBC 4.0 [JDK6] SQL data types

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

95,

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

92, and

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

5. To retrieve a national character value, an application can call one of the following methods:

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 94
INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 95
INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 96

The

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

95 method verifies that the retrieved value is indeed an

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

5. Otherwise, these methods are equivalent to corresponding methods without the letter

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

75.

To specify a value for a parameter marker of national character type, an application can call one of the following methods:

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 00
SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 01
SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 02

These methods are equivalent to corresponding methods without the letter

maximum number of bytes = [maximum number of characters] x [maximum number of bytes for each character]

75 preceded by a call to

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

04.

7.5.3 Using the SQL NCHAR Data Types Without Changing the Code

A Java system property has been introduced in the Oracle JDBC drivers for customers to tell whether the form of use argument should be specified by default in a Java application. This property has the following purposes:

Existing applications accessing the SQL INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 4 data types can be migrated to support the SQL INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3 data types for worldwide deployment without changing a line of code.
Applications do not need to call the INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 75 method when binding and defining a SQL INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3 column. The application code can be made neutral and independent of the data types being used in the back-end database. With this property set, applications can be easily switched from using SQL INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 4 or SQL INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate]; 3.

The Java system property is specified in the command line that invokes the Java application. The syntax of specifying this flag is as follows:

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

With this property specified, the Oracle JDBC drivers assume the presence of the form of use argument for all bind and define operations in the application.

If you have a database schema that consists of both the SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 columns, then using this flag may have some performance impact when accessing the SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 columns because of implicit conversion done in the database server.

7.5.4 Using SQL NCHAR String Literals in JDBC

When using

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 string literals in JDBC, there is a potential for data loss because characters are converted to the database character set before processing. See "" for more details.

The desired behavior for preserving the

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 string literals can be achieved by enabling the property set

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

16. If the value is true, then this option is enabled; otherwise, it is disabled. The default setting is false. It can be enabled in two ways: a] as a Java system property or b] as a connection property. Once enabled, conversion is performed on all SQL in the VM [system property] or in the connection [connection property]. For example, the property can be set as a Java system property as follows:

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

Alternatively, you can set this as a connection property as follows:

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

If you set this as a connection property, it overrides a system property setting.

7.5.5 Data Conversion in JDBC

7.5.5.1 Data Conversion for the OCI Driver

For the OCI driver, the SQL statements are always converted to the database character set by the driver before it is sent to the database for processing. When the database character set is neither US7ASCII nor WE8ISO8859P1, the driver converts the SQL statements to UTF-8 first in Java and then to the database character set in C. Otherwise, it converts the SQL statements directly to the database character set. For Java string bind variables, The following table summarizes the conversion paths taken for different scenarios. For Java string define variables, the same conversion paths, but in the opposite direction, are taken.

Table 7-5 OCI Driver Conversion Path

Form of Use SQL Data Type Conversion Path

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

Conversion between the UTF-16 encoding of a Java string and the database character set happens in the JDBC driver.

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

Conversion between the UTF-16 encoding of a Java string and the database character set happens in the JDBC driver. Then, conversion between the database character set and the national character set happens in the database server.

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

Conversion between the UTF-16 encoding of a Java string and the national character set happens in the JDBC driver.

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

Conversion between the UTF-16 encoding of a Java string and the national character set happens in the JDBC driver. Then, conversion between the national character set and the database character set happens in the database server.

7.5.5.2 Data Conversion for Thin Drivers

SQL statements are always converted to either the database character set or to UTF-8 by the driver before they are sent to the database for processing. The driver converts the SQL statement to the database character set when the database character set is one of the following character sets:

US7ASCII
WE8ISO8859P1
WE8DEC
WE8MSWIN1252

Otherwise, the driver converts the SQL statement to UTF-8 and notifies the database that the statement requires further conversion before being processed. The database, in turn, converts the SQL statement to the database character set. For Java string bind variables, the conversion paths shown in the following table are taken for the thin driver. For Java string define variables, the same conversion paths but in the opposite direction are taken. The four character sets listed earlier are called selected characters sets in the table.

Table 7-6 Thin Driver Conversion Path

Form of Use SQL Data Type Database Character Set Conversion Path

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

One of the selected character sets

Conversion between the UTF-16 encoding of a Java string and the database character set happens in the thin driver.

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

One of the selected character sets

Conversion between the UTF-16 encoding of a Java string and the database character set happens in the thin driver. Then, conversion between the database character set and the national character set happens in the database server.

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

Other than the selected character sets

Conversion between the UTF-16 encoding of a Java string and UTF-8 happens in the thin driver. Then, conversion between UTF-8 and the database character set happens in the database server.

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

Other than the selected character sets

Conversion between the UTF-16 encoding of a Java string and UTF-8 happens in the thin driver. Then, conversion from UTF-8 to the database character set and then to the national character set happens in the database server.

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

Any

Conversion between the UTF-16 encoding of a Java string and the national character set happens in the thin driver. Then, conversion between the national character set and the database character set happens in the database server.

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

Any

Conversion between the UTF-16 encoding of a Java string and the national character set happens in the thin driver.

7.5.5.3 Data Conversion for the Server-Side Internal Driver

All data conversion occurs in the database server because the server-side internal driver works inside the database.

7.5.6 Using oracle.sql.CHAR in Oracle Object Types

JDBC drivers support Oracle object types. Oracle objects are always sent from database to client as an object represented in the database character set or national character set. That means the data conversion path in "" does not apply to Oracle object access. Instead, the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

37 class is used for passing SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

4 and SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data of an object type from the database to the client.

This section includes the following topics:

7.5.6.1 oracle.sql.CHAR

The

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

37 class has a special functionality for conversion of character data. The Oracle character set is a key attribute of the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

37 class. The Oracle character set is always passed in when an

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

37 object is constructed. Without a known character set, the bytes of data in the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

37 object are meaningless.

The

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

37 class provides the following methods for converting character data to strings:

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 45 Converts the sequence of characters represented by the SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 37 object to a string, returning a Java string object. If the character set is not recognized, then SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 45 returns a SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 48.
SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 49 Identical to SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 45, except that if the character set is not recognized, then SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 49 returns a hexadecimal representation of the SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 37 data and does not returns a SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 48.
SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 54 Identical to SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 45, except that a default replacement character replaces characters that have no Unicode representation in the character set of this SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 37 object. This default character varies among character sets, but it is often a question mark.

You may want to construct an

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

37 object yourself [to pass into a prepared statement, for example]. When you construct an

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

37 object, you must provide character set information to the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

37 object by using an instance of the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

60 class. Each instance of the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

60 class represents one of the character sets that Oracle supports.

Complete the following tasks to construct an

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

37 object:

Create a SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 63 instance by calling the static SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 64 method. This method creates the character set class. It requires as input a valid Oracle character set [ SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 65. For example: CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 2 Each character set that Oracle supports has a unique predefined SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 66. The SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 66 can always be referenced as a character set specified as SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 68 SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 69 where SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 68 is the Oracle character set.
Construct an SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 37 object. Pass to the constructor a string [or the bytes that represent the string] and the SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 63 object that indicates how to interpret the bytes based on the character set. For example: CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE]; 3 The SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 37 class has multiple constructors: they can take a string, a byte array, or an object as input along with the SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 63 object. In the case of a string, the string is converted to the character set indicated by the SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 63 object before being placed into the SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%'; 37 object.

The server [database] and the client [or application running on the client] can use different character sets. When you use the methods of this class to transfer data between the server and the client, the JDBC drivers must convert the data between the server character set and the client character set.

7.5.6.2 Accessing SQL CHAR and NCHAR Attributes with oracle.sql.CHAR

The following is an example of an object type created using SQL:

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

The Java class corresponding to this object type can be constructed as follows:

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

The

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

37 class is used here to map to the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

78 attributes of the Oracle object type, which is of

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

9 data type. JDBC populates this class with the byte representation of the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

9 data in the database and the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

63 object corresponding to the database character set. The following code retrieves a

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

82 object from the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

83 table:

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

The

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

45 method of the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

37 class converts the byte array from the database character set or national character set to UTF-16 by calling Oracle's Java data conversion classes and returning a Java string. For the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

86 call to work, the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

87 interface has to be implemented in the class

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

82, and the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

90 has to be set up to indicate the mapping of the object type

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

91 to the Java class.

7.5.7 Restrictions on Accessing SQL CHAR Data with JDBC

7.5.7.1 Character Integrity Issues in a Multibyte Database Environment

Oracle JDBC drivers perform character set conversions as appropriate when character data is inserted into or retrieved from the database. The drivers convert Unicode characters used by Java clients to Oracle database character set characters, and vice versa. Character data that makes a round trip from the Java Unicode character set to the database character set and back to Java can suffer some loss of information. This happens when multiple Unicode characters are mapped to a single character in the database character set. An example is the Unicode full-width tilde character [0xFF5E] and its mapping to Oracle's JA16SJIS character set. The round-trip conversion for this Unicode character results in the Unicode character 0x301C, which is a wave dash [a character commonly used in Japan to indicate range], not a tilde.

The following figure shows the round-trip conversion of the tilde character.

This issue is not a bug in Oracle's JDBC. It is an unfortunate side effect of the ambiguity in character mapping specifications on different operating systems. Fortunately, this problem affects only a small number of characters in a small number of Oracle character sets such as JA16SJIS, JA16EUC, ZHT16BIG5, and KO16KS5601. The workaround is to avoid making a full round-trip with these characters.

7.6 ODBC and OLE DB Programming with Unicode

7.6.1 Unicode-Enabled Drivers in ODBC and OLE DB

Oracle's ODBC driver and Oracle Provider for OLE DB can handle Unicode data properly without data loss. For example, you can run a Unicode ODBC application containing Japanese data on English Windows if you install Japanese fonts and an input method editor for entering Japanese characters.

Oracle provides ODBC and OLE DB products for Windows platforms only. For UNIX platforms, contact your vendor.

7.6.2 OCI Dependency in Unicode

OCI Unicode binding and defining features are used by the ODBC and OLE DB drivers to handle Unicode data. OCI Unicode data binding and defining features are independent from

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26. This means Unicode data is handled properly, irrespective of the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 setting on the platform.

7.6.3 ODBC and OLE DB Code Conversion in Unicode

In general, no redundant data conversion occurs unless you specify a different client data type from that of the server. If you bind Unicode buffer

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

94 with a Unicode data column like

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3, for example, then ODBC and OLE DB drivers bypass it between the application and OCI layer.

If you do not specify data types before fetching, but call

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

96 with the client data types instead, then the conversions described in the following table occur.

Table 7-7 ODBC Implicit Binding Code Conversions

Data Types of ODBC Client Buffer Data Types of the Target Column in the Database Fetch Conversions Comments

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

SELECT CONCAT[name,id] FROM customers;

If the database character set is a subset of the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set, then the conversions occur in the following order:

Database character set
CREATE TABLE table2 [column2 NVARCHAR2[2000]]; 26
UTF-16 in OCI
UTF-16 in ODBC

No unexpected data loss

May degrade performance if database character set is a subset of the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set

NAME

John Smith

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

SELECT CONCAT[name,id] FROM customers;

If database character set is a subset of

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set:

Database character set to

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 in OCI

If database character set is NOT a subset of

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set:

Database character set, UTF-16, to

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set in OCI and ODBC

No unexpected data loss

May degrade performance if database character set is not a subset of

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set

You must specify the data type for inserting and updating operations.

The data type of the ODBC client buffer is given when you call

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

96 but not immediately. Hence,

NAME

John Smith

12 does not have the information.

Because the ODBC driver guarantees data integrity, if you perform implicit bindings, then redundant conversion may result in performance degradation. Your choice is the trade-off between performance with explicit binding or usability with implicit binding.

7.6.3.1 OLE DB Code Conversions

Unlike ODBC, OLE DB only enables you to perform implicit bindings for inserting, updating, and fetching data. The conversion algorithm for determining the intermediate character set is the same as the implicit binding cases of ODBC.

Table 7-8 OLE DB Implicit Bindings

Data Types of OLE_DB Client Buffer Data Types of the Target Column in the Database In-Binding and Out-Binding Conversions Comments

NAME

John Smith

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

SELECT CONCAT[name,id] FROM customers;

If database character set is a subset of the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set:

Database character set to and from

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set in OCI.

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set to UTF-16 in OLE DB

If database character set is NOT a subset of

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set:

Database character set to and from UTF-16 in OCI

No unexpected data loss

May degrade performance if database character set is a subset of

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set

NAME

John Smith

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

SELECT CONCAT[name,id] FROM customers;

If database character set is a subset of the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set:

Database character set to and from

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 in OCI

If database character set is not a subset of

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set:

Database character set to and from UTF-16 in OCI. UTF-16 to

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set in OLE DB

No unexpected data loss

May degrade performance if database character set is not a subset of

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

26 character set

7.6.4 ODBC Unicode Data Types

In ODBC Unicode applications, use

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

1 to store Unicode data. All standard Windows Unicode functions can be used for

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

1 data manipulations. For example,

NAME

John Smith

31 counts the number of characters of

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

1 data:

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

Microsoft's ODBC 3.5 specification defines three Unicode data type identifiers for the

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

94,

NAME

John Smith

34, and

NAME

John Smith

35 clients; and three Unicode data type identifiers for servers

NAME

John Smith

36,

NAME

John Smith

37, and

NAME

John Smith

35.

For binding operations, specify data types for both client and server using

NAME

John Smith

39. The following is an example of Unicode binding, where the client buffer

NAME

John Smith

40 indicates that Unicode data [

SELECT name FROM customers WHERE TO_CHAR[name] LIKE '%Sm%';

is bound to the first bind variable associated with the Unicode column [

NAME

John Smith

36]:

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

The following table represents the data type mappings of the ODBC Unicode data types for the server against SQL

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

3 data types.

Table 7-9 Server ODBC Unicode Data Type Mapping

ODBC Data Type Oracle Data Type

NAME

John Smith

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

NAME

John Smith

NAME

John Smith

NAME

John Smith

SELECT INSTR[name, N'Sm', 1, 1] FROM customers;

According to ODBC specifications,

NAME

John Smith

36,

NAME

John Smith

37, and

NAME

John Smith

35 are treated as Unicode data, and are therefore measured in the number of characters instead of the number of bytes.

7.6.5 OLE DB Unicode Data Types

OLE DB offers the

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

71,

NAME

John Smith

54, and

NAME

John Smith

55 data types for a Unicode C client. In practice,

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

71 is the most common data type and the others are for specific purposes. The following example assigns a static SQL statement:

CREATE TABLE customers [id NUMBER, name NVARCHAR2[50], address NVARCHAR2[200], birthdate DATE];

The

NAME

John Smith

55 macro works exactly like an "L" modifier to indicate the Unicode string. If you need to allocate Unicode data buffer dynamically using

NAME

John Smith

55, then use the

NAME

John Smith

59 allocator [for example,

NAME

John Smith

60]. However, using

NAME

John Smith

55 is not the normal method for variable length data; use

CREATE TABLE table2 [column2 NVARCHAR2[2000]];

71* instead for generic string types.

NAME

John Smith

54 is similar. It is a string with a length prefix in the memory location preceding the string. Some functions and methods can accept only

NAME

John Smith

54 Unicode data types. Therefore,

NAME

John Smith

54 Unicode string must be manipulated with special functions like

NAME

John Smith

66 for allocation and

NAME

John Smith

67 for freeing memory.

Unlike ODBC, OLE DB does not allow you to specify the server data type explicitly. When you set the client data type, the OLE DB driver automatically performs data conversion if necessary.

The following table shows the OLE DB data type mapping.

Table 7-10 OLE DB Data Type Mapping

OLE DB Data Type Oracle Data Type

NAME

John Smith

NAME

John Smith

NAME

John Smith

70 is specified, then it is assumed to be

NAME

John Smith

13 because both are Unicode strings.

7.6.6 ADO Access

ADO is a high-level API to access database with the OLE DB and ODBC drivers. Most database application developers use the ADO interface on Windows because it is easily accessible from Visual Basic, the primary scripting language for Active Server Pages [ASP] for the Internet Information Server [IIS]. To OLE DB and ODBC drivers, ADO is simply an OLE DB consumer or ODBC application. ADO assumes that OLE DB and ODBC drivers are Unicode-aware components; hence, it always attempts to manipulate Unicode data.

7.7 XML Programming with Unicode

XML support of Unicode is essential for software development for global markets so that text information can be exchanged in any language. Unicode uniformly supports almost every character and language, which makes it much easier to support multiple languages within XML. To enable Unicode for XML within an Oracle database, the character set of the database must be UTF-8. By enabling Unicode text handling in your application, you acquire a basis for supporting any language. Every XML document is Unicode text and potentially multilingual, unless it is guaranteed that only a known subset of Unicode characters will appear on your documents. Thus Oracle recommends that you enable Unicode for XML. Unicode support comes with Java and many other modern programming environments.

This section includes the following topics:

7.7.1 Writing an XML File in Unicode with Java

A common mistake in reading and writing XML files is using the

NAME

John Smith

72 and

NAME

John Smith

73 classes for character input and output. Using

NAME

John Smith

72 and

NAME

John Smith

73 for XML files should be avoided because it requires character set conversion based on the default character encoding of the run-time environment.

For example, using

NAME

John Smith

76 class is not safe because it converts the document to the default character encoding. The output file can suffer from a parsing error or data loss if the document contains characters that are not available in the default character encoding.

UTF-8 is popular for XML documents, but UTF-8 is not usually the default file encoding for Java. Thus using a Java class that assumes the default file encoding can cause problems.

The following example shows how to avoid these problems:

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

7.7.2 Reading an XML File in Unicode with Java

Do not read XML files as text input. When reading an XML document stored in a file system, use the parser to automatically detect the character encoding of the document. Avoid using a

NAME

John Smith

72 class or specifying a character encoding on the input stream. Given a binary input stream with no external encoding information, the parser automatically figures out the character encoding based on the byte order mark and encoding declaration of the XML document. Any well-formed document in any supported encoding can be successfully parsed using the following sample code:

INSERT INTO customers VALUES [1000, TO_NCHAR['John Smith'],N'500 Oracle Parkway',sysdate];

7.7.3 Parsing an XML Stream in Unicode with Java

When the source of an XML document is not a file system, the encoding information is usually available before reading the document. For example, if the input document is provided in the form of a Java character stream or Reader, its encoding is evident and no detection should take place. The parser can begin parsing a Reader in Unicode without regard to the character encoding.

7.1.1 Database Access Product Stack and Unicode

7.2 SQL and PL/SQL Programming with Unicode

7.2.1 SQL NCHAR Data Types

7.2.2 Implicit Data Type Conversion Between NCHAR and Other Data Types

7.2.3 Exception Handling for Data Loss During Data Type Conversion

7.2.4 Rules for Implicit Data Type Conversion

7.2.5 SQL Functions for Unicode Data Types

7.2.6 Other SQL Functions

7.2.7 Unicode String Literals

7.2.8 NCHAR String Literal Replacement

7.2.9 Using the UTL_FILE Package with NCHAR Data

7.3 OCI Programming with Unicode

7.3.1 OCIEnvNlsCreate[] Function for Unicode Programming

7.3.2 OCI Unicode Code Conversion

7.3.3 Setting UTF-8 to the NLS_LANG Character Set in OCI

7.3.4 Binding and Defining SQL CHAR Data Types in OCI

7.3.5 Binding and Defining SQL NCHAR Data Types in OCI

7.3.6 Handling SQL NCHAR String Literals in OCI

7.3.7 Binding and Defining CLOB and NCLOB Unicode Data in OCI

7.4 Pro*C/C++ Programming with Unicode

7.4.1 Pro*C/C++ Data Conversion in Unicode

7.4.2 Using the VARCHAR Data Type in Pro*C/C++

7.4.3 Using the NVARCHAR Data Type in Pro*C/C++

7.4.4 Using the UVARCHAR Data Type in Pro*C/C++

7.5 JDBC Programming with Unicode

7.5.1 Binding and Defining Java Strings to SQL CHAR Data Types

7.5.2 Binding and Defining Java Strings to SQL NCHAR Data Types

7.5.3 Using the SQL NCHAR Data Types Without Changing the Code

7.5.4 Using SQL NCHAR String Literals in JDBC

7.5.5 Data Conversion in JDBC

7.5.6 Using oracle.sql.CHAR in Oracle Object Types

7.5.7 Restrictions on Accessing SQL CHAR Data with JDBC

7.6 ODBC and OLE DB Programming with Unicode

7.6.1 Unicode-Enabled Drivers in ODBC and OLE DB

7.6.2 OCI Dependency in Unicode

7.6.3 ODBC and OLE DB Code Conversion in Unicode

7.6.4 ODBC Unicode Data Types

7.6.5 OLE DB Unicode Data Types

7.6.6 ADO Access

7.7 XML Programming with Unicode

7.7.1 Writing an XML File in Unicode with Java

7.7.2 Reading an XML File in Unicode with Java

7.7.3 Parsing an XML Stream in Unicode with Java

Bài Viết Liên Quan

Toplist mới

Bài mới nhất

Chủ Đề