This system catalog 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.) See under CREATE TABLE for more information.
Note: NOT NULL constraints are represented in the pg_attribute catalog.
CHECK constraints on domains are stored here, too. Global ASSERTIONS (a currently-unsupported SQL feature) may someday appear here as well.
Table 3-10. 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 | boolean | Is the constraint deferrable? | |
| condeferred | boolean | 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 |
| 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: pg_class.relchecks needs to agree with the number of check-constraint entries found in this table for the given relation.