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 55.14. pg_constraint
Columns
Column Type Description |
---|
Row identifier |
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 be false only for foreign keys and CHECK constraints |
The table this constraint is on; zero if not a table constraint |
The domain this constraint is on; zero if not a domain constraint |
The index supporting this constraint, if it's a unique, primary key, foreign key, or exclusion constraint; else zero |
The corresponding constraint of the parent partitioned table, if this is a constraint on a partition; else zero |
If a foreign key, the referenced table; else zero |
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 a foreign key with a |
If an exclusion constraint, list of the per-column exclusion operators |
If a check constraint, an internal representation of the
expression. (It's recommended to use
|
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.)
pg_class.relchecks
needs to agree with the
number of check-constraint entries found in this table for each
relation.