pg_constraint

The pg_constraint system catalog table stores check 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.

Table 1. pg_catalog.pg_constraint

column	type	references	description
`conname`	name		Constraint name
`connamespace`	oid	pg_namespace.oid	The OID of the namespace (schema) that contains this constraint.
`contype`	char		`c` = check constraint, `f` = foreign key 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`	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.
`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.