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 44-13. 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 |
| 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 |
| 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.
Note: pg_class.relchecks needs to agree with the number of check-constraint entries found in this table for each relation.