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.
|Row identifier (hidden attribute; must be explicitly selected)|
|Constraint name (not necessarily unique!)|
|The OID of the namespace that contains this constraint|
|Is the constraint deferrable?|
|Is the constraint deferred by default?|
|Has the constraint been validated? Currently, can only be false for foreign keys and CHECK constraints|
|The table this constraint is on; 0 if not a table constraint|
|The domain this constraint is on; 0 if not a domain constraint|
|The index supporting this constraint, if it's a unique, primary key, foreign key, or exclusion constraint; else 0|
|If a foreign key, the referenced table; else 0|
|Foreign key update action code: |
|Foreign key deletion action code: |
|Foreign key match type: |
|This constraint is defined locally for the relation. Note that a constraint can be locally defined and inherited simultaneously.|
|The number of direct inheritance ancestors this constraint has. A constraint with a nonzero number of ancestors cannot be dropped nor renamed.|
|This constraint is defined locally for the relation. It is a non-inheritable constraint.|
|If a table constraint (including foreign keys, but not constraint triggers), list of the constrained columns|
|If a foreign key, list of the referenced columns|
|If a foreign key, list of the equality operators for PK = FK comparisons|
|If a foreign key, list of the equality operators for PK = PK comparisons|
|If a foreign key, list of the equality operators for FK = FK comparisons|
|If an exclusion constraint, list of the per-column exclusion operators|
|If a check constraint, an internal representation of the expression|
|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
indkey for the index.)
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.
pg_class.relchecks needs to agree with the number of check-constraint entries found in this table for each relation.