![]() One way of overcoming this limitation is to perform an UPDATE query using a dummy operation. It is also important to realize that altering a CHECK constraint does not cause existing database rows to be revalidated CHECK constraints are only validated when an INSERT or UPDATE is performed. ![]() ADD CHECK does not replace the current constraint with the new one. Please note that if you want to change the CHECK constraint for a domain that already has a constraint defined, the existing constraint must first be dropped and then the new one added. It is only necessary to name constraints, if they are to be deactivated at a later date using the ALTER TABLE DROP statement. All constraint names are stored in a system table called DB$RELATION_CONSTRAINTS. If no name is specified, Firebird/InterBase ® generates a name automatically. The specification of the keyword CONSTRAINT and the name are optional for all constraints. If the column is based on a domain containing a constraint, both check constraints are active. Only one constraint is permitted per column. ![]() Referential integrity declarations and primary key definitions are special check constraint compositions. The Check Value options permit diverse operations (please refer to Comparison Operators for a full list of possible operators). The value examination is generally performed when inserting or updating this table column. In a check definition the VALUE keyword represents the value of the respective table column.
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