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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

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, t = constraint trigger, x = exclusion constraint
condeferrable bool   Is the constraint deferrable?
condeferred bool   Is the constraint deferred by default?
convalidated bool   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: a = no action, r = restrict, c = cascade, n = set null, d = set default
confdeltype char   Foreign key deletion action code: a = no action, r = restrict, c = cascade, n = set null, d = set default
confmatchtype char   Foreign key match type: f = full, p = partial, u = simple (unspecified)
conislocal bool   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 (including foreign keys, but not constraint triggers), list of the constrained columns
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 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
consrc text   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.