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  5. PG_CONSTRAINT

PG_CONSTRAINT

PG_CONSTRAINT stores check, primary key, unique, and foreign key constraints on 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.

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 and does not track renaming of columns. 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 needs to be consistent with the number of check-constraint entries found in this table for specific relationship.