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41.10. pg_constraint

The catalog pg_constraint stores check, primary key, unique, and foreign key 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.

Check constraints on domains are stored here, too.

Table 41-10. pg_constraint Columns

Name Type References Description
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
condeferrable bool   Is the constraint deferrable?
condeferred bool   Is the constraint deferred by default?
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
confrelid oid pg_class.oid If a foreign key, the referenced table; else 0
confupdtype char   Foreign key update action code
confdeltype char   Foreign key deletion action code
confmatchtype char   Foreign key match type
conkey int2[] pg_attribute.attnum If a table constraint, list of columns which the constraint constrains
confkey int2[] pg_attribute.attnum If a foreign key, list of the referenced columns
conbin text   If a check constraint, an internal representation of the expression
consrc text   If a check constraint, a human-readable representation of the expression

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 the given relation.

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