| Postgres-XC 1.0.1 Documentation | ||||
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Note: The following description applies both to Postgres-XC and PostgreSQL if not described explicitly.
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 45-12. 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, 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? Can only be false for foreign keys | |
| 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, u = simple (unspecified) | |
| 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. | |
| 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.