Oracle PL/SQL Programming, 5th Edition

String Datatypes

Oracle supports four string datatypes, summarized in the following table. Which type you should use depends on your answers to the following two questions:

• Are you working with variable-length or fixed-length strings?

• Do you want to use the database character set or the national character set?

	Fixed-length	Variable-length
Database character set	CHAR	VARCHAR2
National character set	NCHAR	NVARCHAR2

You will rarely need or want to use the fixed-length CHAR and NCHAR datatypes in Oracle-based applications; in fact, I recommend that you never use these types unless there is a specific requirement for fixed-length strings. See Mixing CHAR and VARCHAR2 Values for a description of problems you may encounter when mixing fixed- and variable-length string variables. (The NCHAR and NVARCHAR2 datatypes are discussed in Chapter 25.)

The VARCHAR2 Datatype

VARCHAR2 variables store variable-length character strings. When you declare a variable-length string, you must also specify a maximum length for the string, which can range from 1 to 32,767 bytes. You may specify the maximum length in terms of characters or bytes, but either way the length is ultimately defined in bytes. The general format for a VARCHAR2 declaration is:

variable_name VARCHAR2 (max_length [CHAR | BYTE]);

where:

variable_name

Is the name of the variable you want to declare.

max_length

Is the maximum length of the variable.

CHAR

Indicates that max_length is expressed in terms of characters.

BYTE

Indicates that max_length represents ...