Difference between revisions of "NULL Column Constraint"

Revision as of 17:37, 8 December 2009

Purpose

Column constraint to allow NULL values

Syntax

NULL

See Also

ALTER TABLE, CONSTRAINTS, CREATE TABLE

Description

A constraint is used to define rules that help to provide data integrity. Column constraints are specific to the column name specified. You must have ALTER privilege on the table. The table will be locked for EXCLUSIVE use during the operation.

The NULL column constraint is used to specify that the column can contain NULL values. The NOT NULL column constraint can be used to disallow NULL values.

Example

set sql to recital
exec sql
ALTER TABLE customer ADD COLUMN custref char(5) NULL;
exec sql
ALTER TABLE customer ALTER COLUMN custref NOT NULL;
use customer
list dictionary

Products

Recital, Recital Server