NULL Column Constraint

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NULL

Class

Column Constraints


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 Database Server, Recital Mirage Server, Recital Terminal Developer