There are several ways to alter the existing set of CHECK constraints on a table.
ALTER TABLE Customers ALTER Phone CHECK NULL;
ALTER TABLE Customers ALTER Phone CHECK ( Phone LIKE '___-___-____' );
To use the ALTER TABLE statement with the DELETE CHECK clause:
ALTER TABLE table-name DELETE CHECK;
Sybase Central lets you add, alter and drop both table and column CHECK constraints. For more information, see Working with table and column constraints in Sybase Central.
Dropping a column from a table does not drop CHECK constraints associated with the column held in the table constraint. Not
removing the constraints produces a
column not found error message upon any attempt to insert, or even just query, data in the table.
Table CHECK constraints fail if a value of FALSE is returned. If the condition returns a value of UNKNOWN the behavior is as though it returned TRUE, and the value is allowed.
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