PG_CONSTRAINT

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

**Table 1** PG_CONSTRAINT columns
Name	Type	Description
conname	name	Constraint name (not necessarily unique)
connamespace	oid	OID of the namespace that contains the constraint
contype	"char"	c indicates check constraints. f indicates foreign key constraints. p indicates primary key constraints. u indicates unique constraints. t indicates trigger constraints.
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, only foreign key and check constraints can be set to false.
conrelid	oid	Table containing this constraint. The value is 0 if it is not a table constraint.
contypid	oid	Domain containing this constraint. The value is 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.
confupdtype	"char"	Foreign key update action code a indicates no action. r indicates restriction. c indicates cascading. n indicates that the parameter is set to null. d indicates that the default value is used.
confdeltype	"char"	Foreign key deletion action code a indicates no action. r indicates restriction. c indicates cascading. n indicates that the parameter is set to null. d indicates that the default value is used.
confmatchtype	"char"	Foreign key match type f indicates full match. p indicates partial match. u indicates simple match (not specified).
conislocal	boolean	Whether the local constraint is defined for the relationship
coninhcount	integer	Number of direct inheritance parent tables this constraint has. When the number 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 Informational Constraint to optimize the execution plan.
conkey	smallint[]	Column list of the constrained control if this column is a table constraint
confkey	smallint[]	List of referenced columns if this column is a foreign key
conpfeqop	oid[]	ID list of the equality operators for PK = FK comparisons if this column is a foreign key
conppeqop	oid[]	ID list of the equality operators for PK = PK comparisons if this column is a foreign key
conffeqop	oid[]	ID list of the equality operators for FK = FK comparisons if this column is a foreign key
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

consrc is not updated when referenced objects change; for example, it will not 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.
pg_class.relchecks must be consistent with the number of check-constraint entries in this table for each relationship.

Example

Query whether a specified table has a primary key.

    
         CREATE TABLE t1
(    
    C_CUSTKEY    BIGINT       ,
    C_NAME       VARCHAR(25)  ,
    C_ADDRESS    VARCHAR(40)  ,
    C_NATIONKEY  INT          ,
    C_PHONE      CHAR(15)     ,
    C_ACCTBAL    DECIMAL(15,2), 
    CONSTRAINT C_CUSTKEY_KEY PRIMARY KEY(C_CUSTKEY,C_NAME)
)
DISTRIBUTE BY HASH(C_CUSTKEY,C_NAME);

SELECT conname FROM pg_constraint WHERE conrelid = 't1'::regclass AND contype = 'p';
    conname
---------------
 c_custkey_key
(1 row)

Parent topic: System Catalogs

Previous topic: PG_COLLATION

Next topic: PG_CONVERSION

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