51.13. `pg_constraint`
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## 51.13. `pg_constraint` #

The catalog `pg_constraint` stores check, primary key, unique, foreign key, and exclusion constraints on tables, as well as not-null constraints on domains. (Column constraints are not treated specially. Every column constraint is equivalent to some table constraint.) Not-null constraints on relations are represented in the `pg_attribute` catalog, not here.

User-defined constraint triggers (created with `CREATE CONSTRAINT TRIGGER`) also give rise to an entry in this table.

Check constraints on domains are stored here, too.

Table 51.13. `pg_constraint` Columns

Column Type Description
`oid` `oid` Row identifier
`conname` `name` Constraint name (not necessarily unique!)
`connamespace` `oid` (references `pg_namespace`.`oid`) The OID of the namespace that contains this constraint
`contype` `char` `c` = check constraint, `f` = foreign key constraint, `n` = not-null constraint (domains only), `p` = primary key constraint, `u` = unique constraint, `t` = constraint trigger, `x` = exclusion constraint
`condeferrable` `bool` Is the constraint deferrable?
`condeferred` `bool` Is the constraint deferred by default?
`convalidated` `bool` Has the constraint been validated? Currently, can be false only for foreign keys and CHECK constraints
`conrelid` `oid` (references `pg_class`.`oid`) The table this constraint is on; zero if not a table constraint
`contypid` `oid` (references `pg_type`.`oid`) The domain this constraint is on; zero if not a domain constraint
`conindid` `oid` (references `pg_class`.`oid`) The index supporting this constraint, if it's a unique, primary key, foreign key, or exclusion constraint; else zero
`conparentid` `oid` (references `pg_constraint`.`oid`) The corresponding constraint of the parent partitioned table, if this is a constraint on a partition; else zero
`confrelid` `oid` (references `pg_class`.`oid`) If a foreign key, the referenced table; else zero
`confupdtype` `char` Foreign key update action code: `a` = no action, `r` = restrict, `c` = cascade, `n` = set null, `d` = set default
`confdeltype` `char` Foreign key deletion action code: `a` = no action, `r` = restrict, `c` = cascade, `n` = set null, `d` = set default
`confmatchtype` `char` Foreign key match type: `f` = full, `p` = partial, `s` = simple
`conislocal` `bool` This constraint is defined locally for the relation. Note that a constraint can be locally defined and inherited simultaneously.
`coninhcount` `int2` The number of direct inheritance ancestors this constraint has. A constraint with a nonzero number of ancestors cannot be dropped nor renamed.
`connoinherit` `bool` This constraint is defined locally for the relation. It is a non-inheritable constraint.
`conkey` `int2[]` (references `pg_attribute`.`attnum`) If a table constraint (including foreign keys, but not constraint triggers), list of the constrained columns
`confkey` `int2[]` (references `pg_attribute`.`attnum`) If a foreign key, list of the referenced columns
`conpfeqop` `oid[]` (references `pg_operator`.`oid`) If a foreign key, list of the equality operators for PK = FK comparisons
`conppeqop` `oid[]` (references `pg_operator`.`oid`) If a foreign key, list of the equality operators for PK = PK comparisons
`conffeqop` `oid[]` (references `pg_operator`.`oid`) If a foreign key, list of the equality operators for FK = FK comparisons
`confdelsetcols` `int2[]` (references `pg_attribute`.`attnum`) If a foreign key with a `SET NULL` or `SET DEFAULT` delete action, the columns that will be updated. If null, all of the referencing columns will be updated.
`conexclop` `oid[]` (references `pg_operator`.`oid`) If an exclusion constraint, list of the per-column exclusion operators
`conbin` `pg_node_tree` If a check constraint, an internal representation of the expression. (It's recommended to use `pg_get_constraintdef()` to extract the definition of a check constraint.)

In the case of an exclusion constraint, `conkey` is only useful for constraint elements that are simple column references. For other cases, a zero appears in `conkey` and the associated index must be consulted to discover the expression that is constrained. (`conkey` thus has the same contents as `pg_index`.`indkey` for the index.)

### Note

`pg_class.relchecks` needs to agree with the number of check-constraint entries found in this table for each relation.

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