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.
Check constraints on domains are stored here, too.
pg_constraint Columns
| Column Type | Description |
|---|---|
oid oid | Row identifier |
conname name | Constraint name (not necessarily unique!) |
connamespace oid (references 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 be false only for foreign keys and CHECK constraints |
conrelid oid (references pg_class.oid) | The table this constraint is on; zero if not a table constraint |
contypid oid (references pg_type.oid) | The domain this constraint is on; zero if not a domain constraint |
conindid oid (references pg_class.oid) | The index supporting this constraint, if it’s a unique, primary key, foreign key, or exclusion constraint; else zero |
conparentid oid (references pg_constraint.oid) | The corresponding constraint of the parent partitioned table, if this is a constraint on a partition; else zero |
confrelid oid (references pg_class.oid) | If a foreign key, the referenced table; else zero |
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[] (references pg_attribute.attnum) | If a table constraint (including foreign keys, but not constraint triggers), list of the constrained columns |
confkey int2[] (references pg_attribute.attnum) | If a foreign key, list of the referenced columns |
conpfeqop oid[] (references pg_operator.oid) | If a foreign key, list of the equality operators for PK = FK comparisons |
conppeqop oid[] (references pg_operator.oid) | If a foreign key, list of the equality operators for PK = PK comparisons |
conffeqop oid[] (references pg_operator.oid) | If a foreign key, list of the equality operators for FK = FK comparisons |
conexclop oid[] (references 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. (It’s recommended to use pg_get_constraintdef() to extract the definition of a check constraint.) |
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.)
pg_class.relchecks needs to agree with the number of check-constraint entries found in this table for each relation.