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.)
consrcis 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.relchecksneeds to agree with the number of check-constraint entries found in this table for each relation.
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