Gbase 8C system table PG_ constraint

pg_constraint System tables store check constraints on tables 、 Primary key 、 Unique constraints and foreign key constraints .

name	type	quote	describe
oid	oid		Row identifier （ Hidden attribute , Must be explicitly selected to display ）
conname	name		Constraint name （ It doesn't need to be the only one ！）
connamespace	oid	pg_namespace.oid	The name of the namespace containing this constraint OID
contype	char		c = Check constraint , f = Foreign key constraints , p = Primary key constraint , u = Unique constraint , t = Constraint trigger , x = Exclusive constraints
condeferrable	bool		Whether the constraint can be delayed ？
condeferred	bool		Whether the constraint is delayed by default ？
convalidated	bool		Whether this constraint has been verified ？ Currently, foreign keys and check constraints can only be false
conrelid	oid	pg_class.oid	The table where the constraint is located , If it is not a table constraint, it is 0
contypid	oid	pg_type.oid	The domain in which the constraint resides , If it is not a domain constraint, it is 0
conindid	oid	pg_class.oid	If the constraint is unique 、 Primary key 、 Foreign keys or exclusive constraints , This column represents the index that supports this constraint , Otherwise 0
confrelid	oid	pg_class.oid	If this constraint is a foreign key constraint , This column is the referenced table , Otherwise 0
confupdtype	char		Foreign key update action code ： a = No action , r = Limit , c = cascade , n = empty , d = Set to default
confdeltype	char		Foreign key deletion action code ： a = No action , r = Limit , c = cascade , n = empty , d = Set to default
confmatchtype	char		Foreign key matching type ： f = Completely , p = part , s = Simple
conislocal	bool		This constraint is defined locally in the relationship . Note that a constraint can be both locally defined and inherited .
coninhcount	int4		Number of direct inheritance ancestors for this constraint . A non-zero constraint on this column cannot be deleted or renamed .
connoinherit	bool		True means that the constraint is defined locally in the relationship . It is a non inheritable constraint .
conkey	int2[]	pg_attribute.attnum	If it is a table constraint （ Include foreign keys but not constraint triggers ）, This column is a list of constrained Columns
confkey	int2[]	pg_attribute.attnum	If it's a foreign key , This column is a list of referenced Columns
conpfeqop	oid[]	pg_operator.oid	If it's a foreign key , This column is used for PK = FK List of equivalent operators for comparison
conppeqop	oid[]	pg_operator.oid	If it's a foreign key , This column is used for PK = PK List of equivalent operators for comparison
conffeqop	oid[]	pg_operator.oid	If it's a foreign key , This column is used for FK = FK List of equivalent operators for comparison
conexclop	oid[]	pg_operator.oid	If it's an exclusive constraint , This column is a list of non exclusive operators
conbin	pg_node_tree		If it is a check constraint , This column is an internal representation of the expression
consrc	text		If it is a check constraint , This column is a human readable representation of the expression

Be careful ：consrc It will not be updated after the referenced object changes , It does not track field name changes . Instead of relying on this field , It's better to use pg_get_constraintdef() To extract the definition of a check constraint .

pg_class.relchecks It needs to be consistent with the number of check constraints found on this table for a given relationship .