45.12. pg_constraint

The catalog pg_constraint 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, not here.

User-defined constraint triggers (created with CREATE CONSTRAINT TRIGGER) also give rise to an entry in this table.

Check constraints on domains are stored here, too.

Table 45-12. pg_constraint Columns

connamename Constraint name (not necessarily unique!)
connamespaceoidpg_namespace.oid The OID of the namespace that contains this constraint
contypechar  c = check constraint, f = foreign key constraint, p = primary key constraint, u = unique constraint, t = constraint trigger, x = exclusion constraint
condeferrablebool Is the constraint deferrable?
condeferredbool Is the constraint deferred by default?
conrelidoidpg_class.oidThe table this constraint is on; 0 if not a table constraint
contypidoidpg_type.oidThe domain this constraint is on; 0 if not a domain constraint
conindidoidpg_class.oidThe index supporting this constraint, if it's a unique, primary key, foreign key, or exclusion constraint; else 0
confrelidoidpg_class.oidIf a foreign key, the referenced table; else 0
confupdtypechar Foreign key update action code: a = no action, r = restrict, c = cascade, n = set null, d = set default
confdeltypechar Foreign key deletion action code: a = no action, r = restrict, c = cascade, n = set null, d = set default
confmatchtypechar Foreign key match type: f = full, p = partial, u = simple (unspecified)
conislocalbool  This constraint is defined locally for the relation. Note that a constraint can be locally defined and inherited simultaneously.
coninhcountint4  The number of direct inheritance ancestors this constraint has. A constraint with a nonzero number of ancestors cannot be dropped nor renamed.
conkeyint2[]pg_attribute.attnumIf a table constraint (including foreign keys, but not constraint triggers), list of the constrained columns
confkeyint2[]pg_attribute.attnumIf a foreign key, list of the referenced columns
conpfeqopoid[]pg_operator.oidIf a foreign key, list of the equality operators for PK = FK comparisons
conppeqopoid[]pg_operator.oidIf a foreign key, list of the equality operators for PK = PK comparisons
conffeqopoid[]pg_operator.oidIf a foreign key, list of the equality operators for FK = FK comparisons
conexclopoid[]pg_operator.oidIf an exclusion constraint, list of the per-column exclusion operators
conbintext If a check constraint, an internal representation of the expression
consrctext If a check constraint, a human-readable representation of the expression

In the case of an exclusion constraint, conkey is only useful for constraint elements that are simple column references. For other cases, a zero appears in conkey and the associated index must be consulted to discover the expression that is constrained. (conkey thus has the same contents as pg_index.indkey for the index.)

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.

Note: pg_class.relchecks needs to agree with the number of check-constraint entries found in this table for each relation. Also, pg_class.relhasexclusion must be true if there are any exclusion-constraint entries for the relation.