Constant

A constant holds a value that does not change.

A constant declaration specifies the name, data type, and value of the constant and allocates storage for it. The declaration can also impose the NOT NULL constraint.

Topics:

Syntax
Semantics
Examples
Related Topics

Syntax

constant_declaration ::=

Description of the illustration constant_declaration.gif

See expression ::=.

datatype ::=

Description of the illustration datatype.gif

Semantics

constant_declaration

constant_name

The name of the constant that you are declaring.

NOT NULL

Prevents the program from assigning the value NULL to the constant.

PL/SQL subtypes NATURALN, POSITIVEN, and SIMPLE_INTEGER are predefined as NOT NULL. When declaring a constant of one of these subtypes, you can omit NOT NULL.

If you declare a NOT NULL constant, either by specifying NOT NULL or by specifying a subtype that is predefined as NOT NULL, you must also specify an initial value for the constant.

expression

The initial value for the constant. The value of expression must have a data type that is compatible with datatype (see Table 3-10, "Possible Implicit PL/SQL Data Type Conversions"). When constant_declaration is elaborated, the value of expression is assigned to constant_name.

datatype

collection_name

The name of a collection.

collection_type_name

The name of a user-defined collection type defined with the data type specifier TABLE or VARRAY.

cursor_name

The name of an explicit cursor.

cursor_variable_name

The name of a cursor variable.

db_table_name

The name of a database table or view, which must be accessible when the declaration is elaborated.

column_name

The name of a column of the database table or view db_table_name.

object_name

An instance of a user-defined type.

object_type_name

The name of a user-defined type.

record_name

The name of a record.

field_name

The name of a field of record_name.

record_type_name

The name of a user-defined type that was defined with the data type specifier RECORD.

ref_cursor_type_name

The name of a user-defined type that was defined with the data type specifier REF CURSOR.

scalar_datatype_name

The name of a predefined scalar data type, including any qualifiers for size, precision, and character or byte semantics. For information about predefined scalar data types, see "Predefined PL/SQL Scalar Data Types and Subtypes".

variable_name

The name of a variable.

Examples