Difference between revisions of "CHECK Column Constraint"
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==Purpose== | ==Purpose== | ||
Column constraint to validate a change to the value of a column | Column constraint to validate a change to the value of a column | ||
Revision as of 15:09, 29 October 2009
Purpose
Column constraint to validate a change to the value of a column
Syntax
CHECK <condition>
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 CHECK column constraint is used to validate any changes made to the value of a column. The <condition> specified must evaluate to True (.T.) for the modification operation to succeed. If the <condition> evaluates to False (.F.) the column value remains unchanged and the ERROR column constraint message is displayed. If the ERROR column constraint has not been defined, a default error message is displayed.
Example
set sql to recital exec sql ALTER TABLE customer ADD COLUMN timeref char(8) CHECK validtime(timeref) ERROR "Not a valid time string"; use customer edit
Products
Recital Database Server, Recital Mirage Server, Recital Terminal Developer
