51.13. 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.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.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, 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.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.