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The pg_constraint system catalog table 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 table. Check constraints on domains are stored here, too.
| column | type | references | description |
|---|---|---|---|
conname | name | Constraint name (not necessarily unique!) | |
connamespace | oid | pg_namespace.oid | The OID of the namespace (schema) 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. This is not updated when referenced objects change; for example, it won’t track renaming of columns. Rather than relying on this field, it is best to use pg_get_constraintdef() to extract the definition of a check constraint. |
Parent topic: System Catalogs Definitions
