PG_CONSTRAINT

PG_CONSTRAINT records check, primary key, and unique constraints on tables.

Table 1 PG_CONSTRAINT columns

Name	Type	Description
oid	oid	Row identifier (hidden attribute, which must be specified)
conname	name	Constraint name (not necessarily unique)
connamespace	oid	OID of the namespace that contains the constraint
contype	"char"	c: check constraint p: primary key constraint u: unique constraint t: trigger constraint
condeferrable	Boolean	Whether the constraint can be deferrable
condeferred	Boolean	Whether the constraint can be deferrable by default
convalidated	Boolean	Whether the constraint is valid. Currently, it can be set to false only for foreign key and check constraints.
conrelid	oid	Table containing this constraint (0 if it is not a table constraint)
contypid	oid	Domain containing this constraint (0 if it is not a domain constraint)
conindid	oid	ID of the index associated with the constraint
confrelid	oid	Referenced table if this constraint is a foreign key. Otherwise, the value is 0. Currently, foreign keys are not supported. Therefore, the value is fixed at 0.
confupdtype	"char"	Foreign key update action code a: no action r: restriction c: cascading n: The parameter is set to null. d: The default value is used. The value is empty because foreign keys are not supported currently.
confdeltype	"char"	Foreign key deletion action code a: no action r: restriction c: cascading n: The parameter is set to null. d: The default value is used. The value is empty because foreign keys are not supported currently.
confmatchtype	"char"	Foreign key match type f: full match p: partial match u: simple match (not specified) The value is empty because foreign keys are not supported currently.
conislocal	Boolean	Whether the local constraint is defined for the relationship
coninhcount	integer	Number of direct inheritance parent tables that this constraint has. When the value is not 0, the constraint cannot be deleted or renamed.
connoinherit	Boolean	Whether the constraint can be inherited
consoft	Boolean	Whether the column indicates an informational constraint
conopt	Boolean	Whether you can use the informational constraint to optimize the execution plan
conkey	smallint[]	Column list of the constrained control if this column is a table constraint
conincluding	smallint[]	Not for constraint, but will be included in the attribute column of INDEX.
confkey	smallint[]	List of referenced columns if this column is a foreign key. The value is empty because foreign keys are not supported currently.
conpfeqop	oid[]	ID list of the equality operators for PK = FK comparisons if this column is a foreign key. The value is empty because foreign keys are not supported currently.
conppeqop	oid[]	ID list of the equality operators for PK = PK comparisons if this column is a foreign key. The value is empty because foreign keys are not supported currently.
conffeqop	oid[]	ID list of the equality operators for FK = FK comparisons if this column is a foreign key. The value is empty because foreign keys are not supported currently.
conexclop	oid[]	ID list of the per-column exclusion operators if this column is an exclusion constraint
conbin	pg_node_tree	Internal representation of the expression if this column is a check constraint
consrc	text	Human-readable representation of the expression if this column is a check constraint

NOTICE:
consrc is not updated when referenced objects change and does not track new column names. Instead of relying on this column to update, you are advised to use pg_get_constraintdef() to extract the definition of a check constraint.
pg_class.relchecks must agree with the number of check-constraint entries found in the table for each relationship.