pg_constraint

The pg_constraint system catalog table stores check, primary key, unique, and foreign key constraints on tables. Column constraints are not treated specially. Every column constraint is equivalent to some table constraint. Not-null constraints are represented in the pg_attribute catalog table. Check constraints on domains are stored here, too.

column	type	references	description
conname	name		Constraint name (not necessarily unique!)
connamespace	oid	pg_namespace.oid	The OID of the namespace (schema) that contains this constraint.
contype	char		c = check constraint, f = foreign key constraint, p = primary key constraint, u = unique constraint.
condeferrable	boolean		Is the constraint deferrable?
condeferred	boolean		Is the constraint deferred by default?
conrelid	oid	pg_class.oid	The table this constraint is on; 0 if not a table constraint.
contypid	oid	pg_type.oid	The domain this constraint is on; 0 if not a domain constraint.
confrelid	oid	pg_class.oid	If a foreign key, the referenced table; else 0.
confupdtype	char		Foreign key update action code.
confdeltype	char		Foreign key deletion action code.
confmatchtype	char		Foreign key match type.
conkey	int2[]	pg_attribute.attnum	If a table constraint, list of columns which the constraint constrains.
confkey	int2[]	pg_attribute.attnum	If a foreign key, list of the referenced columns.
conbin	text		If a check constraint, an internal representation of the expression.
consrc	text		If a check constraint, a human-readable representation of the expression. This is not updated when referenced objects change; for example, it won't track renaming of columns. Rather than relying on this field, it is best to use pg_get_constraintdef() to extract the definition of a check constraint.

Parent topic: System Catalogs Definitions