System Catalogs Definitions - pg_constraint - 《Greenplum Database v6.23 Documentation》

The pg_constraint system catalog table 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 table. Check constraints on domains are stored here, too.

column	type	references	description
`conname`	name		Constraint name (not necessarily unique!)
`connamespace`	oid	pg_namespace.oid	The OID of the namespace (schema) that contains this constraint.
`contype`	char		`c` = check constraint, `f` = foreign key constraint, `p` = primary key constraint, `u` = unique constraint.
`condeferrable`	boolean		Is the constraint deferrable?
`condeferred`	boolean		Is the constraint deferred by default?
`convalidated`	boolean		Has the constraint been validated? Currently, can only be false for foreign keys
`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.
`confdeltype`	char		Foreign key deletion action code.
`confmatchtype`	char		Foreign key match type.
`conislocal`	boolean		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.
`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.
`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 PK = PK comparisons.
`conexclop`	oid[]	pg_operator.oid	If an exclusion constraint, list of the per-column exclusion operators.
`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. This is not updated when referenced objects change; for example, it won’t track renaming of columns. Rather than relying on this field, it is best to use `pg_get_constraintdef()` to extract the definition of a check constraint.

Parent topic: System Catalogs Definitions