pg_constraint

The pg_constraint system catalog table stores check, primary key, unique, foreign key, and exclusion 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
oid	oid		Row identifier
conname	name	Constraint name (not necessarily unique!)
connamespace	oid	pg_namespace.oid	The object identifier of the namespace (schema) that contains this constraint.
contype	char		c = check constraint, f = foreign key constraint, p = primary key constraint, u = unique constraint, x = exclusion constraint.
condeferrable	boolean		Is the constraint deferrable?
condeferred	boolean		Is the constraint deferred by default?
kconvalidated	boolean		Has the constraint been validated? Currently, can only be false for foreign keys and CHECK constraints.
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
conparentid	oid	pg_constraint.oid	The corresponding constraint in the parent partitioned table, if this is a constraint in a partition; 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	integer		The number of direct inheritance ancestors this constraint has. A constraint with a nonzero number of ancestors cannot be dropped nor renamed.
connoinherit	boolean		This constraint is defined locally for the relation. It is a non-inheritable constraint.
conkey	smallint[]	pg_attribute.attnum	If a table constraint, list of columns which the constraint constrains.
confkey	smallint[]	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 FK = FK comparisons.
conexclop	oid[]	pg_operator.oid	If an exclusion constraint, list of the per-column exclusion operators.
conbin	pg_node_tree		If a check constraint, an internal representation of the expression. (It is recommended to use pg_get_constraintdef() to extract the definition of a check constraint.)