43.13. `pg_constraint`

The catalog pg_constraint 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.

Check constraints on domains are stored here, too.

Table 43-13. pg_constraint Columns

Name	Type	References	Description
`conname`	`name`		Constraint name (not necessarily unique!)
`connamespace`	`oid`	`pg_namespace.oid`	The OID of the namespace that contains this constraint
`contype`	`char`		`c` = check constraint, `f` = foreign key constraint, `p` = primary key constraint, `u` = unique constraint
`condeferrable`	`bool`		Is the constraint deferrable?
`condeferred`	`bool`		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

Note: consrc is not updated when referenced objects change; for example, it won't track renaming of columns. Rather than relying on this field, it's best to use pg_get_constraintdef() to extract the definition of a check constraint.