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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

Column Type

Description

oid oid

Row identifier

conname name

Constraint name (not necessarily unique!)

connamespace oid (references 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 (references pg_class.oid)

The table this constraint is on; 0 if not a table constraint

contypid oid (references pg_type.oid)

The domain this constraint is on; 0 if not a domain constraint

conindid oid (references pg_class.oid)

The index supporting this constraint, if it's a unique, primary key, foreign key, or exclusion constraint; else 0

conparentid oid (references pg_constraint.oid)

The corresponding constraint in the parent partitioned table, if this is a constraint in a partition; else 0

confrelid oid (references 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[] (references pg_attribute.attnum)

If a table constraint (including foreign keys, but not constraint triggers), list of the constrained columns

confkey int2[] (references pg_attribute.attnum)

If a foreign key, list of the referenced columns

conpfeqop oid[] (references pg_operator.oid)

If a foreign key, list of the equality operators for PK = FK comparisons

conppeqop oid[] (references pg_operator.oid)

If a foreign key, list of the equality operators for PK = PK comparisons

conffeqop oid[] (references pg_operator.oid)

If a foreign key, list of the equality operators for FK = FK comparisons

conexclop oid[] (references 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. (It's recommended to use pg_get_constraintdef() to extract the definition of a check constraint.)


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

pg_class.relchecks needs to agree with the number of check-constraint entries found in this table for each relation.