# 52.13. 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. 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 51.13. `pg_constraint` Columns** | Name | Type | References | Description | | --------------- | -------------- | -------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `oid` | `oid` | | Row identifier (hidden attribute; must be explicitly selected) | | `conname` | `name` | | Constraint name (not necessarily unique!) | | `connamespace` | `oid` | [`pg_namespace`](https://www.postgresql.org/docs/10/static/catalog-pg-namespace.html).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 only be false for foreign keys and CHECK constraints | | `conrelid` | `oid` | [`pg_class`](https://www.postgresql.org/docs/10/static/catalog-pg-class.html).oid | The table this constraint is on; 0 if not a table constraint | | `contypid` | `oid` | [`pg_type`](https://www.postgresql.org/docs/10/static/catalog-pg-type.html).oid | The domain this constraint is on; 0 if not a domain constraint | | `conindid` | `oid` | [`pg_class`](https://www.postgresql.org/docs/10/static/catalog-pg-class.html).oid | The index supporting this constraint, if it's a unique, primary key, foreign key, or exclusion constraint; else 0 | | `confrelid` | `oid` | [`pg_class`](https://www.postgresql.org/docs/10/static/catalog-pg-class.html).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, `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[]` | [`pg_attribute`](https://www.postgresql.org/docs/10/static/catalog-pg-attribute.html).attnum | If a table constraint (including foreign keys, but not constraint triggers), list of the constrained columns | | `confkey` | `int2[]` | [`pg_attribute`](https://www.postgresql.org/docs/10/static/catalog-pg-attribute.html).attnum | If a foreign key, list of the referenced columns | | `conpfeqop` | `oid[]` | [`pg_operator`](https://www.postgresql.org/docs/10/static/catalog-pg-operator.html).oid | If a foreign key, list of the equality operators for PK = FK comparisons | | `conppeqop` | `oid[]` | [`pg_operator`](https://www.postgresql.org/docs/10/static/catalog-pg-operator.html).oid | If a foreign key, list of the equality operators for PK = PK comparisons | | `conffeqop` | `oid[]` | [`pg_operator`](https://www.postgresql.org/docs/10/static/catalog-pg-operator.html).oid | If a foreign key, list of the equality operators for FK = FK comparisons | | `conexclop` | `oid[]` | [`pg_operator`](https://www.postgresql.org/docs/10/static/catalog-pg-operator.html).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. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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