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 47-13. pg_constraint Columns
|oid||oid||Row identifier (hidden attribute; must be explicitly selected)|
|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 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|
|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, s = simple|
|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.|
|connoinherit||bool||This constraint is defined locally for the relation. It is a non-inheritable constraint.|
|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.
If you see anything in the documentation that is not correct, does not match your experience with the particular feature or requires further clarification, please use this form to report a documentation issue.