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?
convalidated	boolean		Has the constraint been validated? Currently, can only be false for foreign keys
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.
conindid	oid	pg_class.oid	The index supporting this constraint, if it's a unique, primary key, foreign key, or exclusion constraint; else 0
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.
conislocal	boolean		This constraint is defined locally for the relation. Note that a constraint can be locally defined and inherited simultaneously.
coninhcount	int4		The number of direct inheritance ancestors this constraint has. A constraint with a nonzero number of ancestors cannot be dropped nor renamed.
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.
conpfeqop	oid[]	pg_operator.oid	If a foreign key, list of the equality operators for PK = FK comparisons.
conppeqop	oid[]	pg_operator.oid	If a foreign key, list of the equality operators for PK = PK comparisons.
conffeqop	oid[]	pg_operator.oid	If a foreign key, list of the equality operators for PK = PK comparisons.
conexclop	oid[]	pg_operator.oid	If an exclusion constraint, list of the per-column exclusion operators.
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