---
title: "pg_constraint"
id: catalog-pg-constraint
pg_version: "20devel"
---

<a id="catalog-pg-constraint"></a>

## 52.13. pg_constraint

The catalog pg_constraint stores check, not-null, primary key, unique, foreign key, and exclusion constraints on tables. (Column constraints are not treated specially. Every column constraint is equivalent to some table constraint.) 

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

Check constraints on domains are stored here, too. 

**pg_constraint Columns**

| Column Type | Description | 
| --- | --- |
| `oid` `oid` | Row identifier |
| `conname` `name` | Constraint name (not necessarily unique!) |
| `connamespace` `oid` (references [pg_namespace](catalog-pg-namespace.md).`oid`) | The OID of the namespace that contains this constraint |
| `contype` `char` | `c` = check constraint, `f` = foreign key constraint, `n` = not-null constraint, `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? |
| `conenforced` `bool` | Is the constraint enforced? |
| `convalidated` `bool` | Has the constraint been validated? |
| `conrelid` `oid` (references [pg_class](catalog-pg-class.md).`oid`) | The table this constraint is on; zero if not a table constraint |
| `contypid` `oid` (references [pg_type](catalog-pg-type.md).`oid`) | The domain this constraint is on; zero if not a domain constraint |
| `conindid` `oid` (references [pg_class](catalog-pg-class.md).`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](catalog-pg-constraint.md).`oid`) | The corresponding constraint of the parent partitioned table, if this is a constraint on a partition; else zero |
| `confrelid` `oid` (references [pg_class](catalog-pg-class.md).`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. |
| `conperiod` `bool` | This constraint is defined with `WITHOUT OVERLAPS` (for primary keys and unique constraints) or `PERIOD` (for foreign keys). |
| `conkey` `int2[]` (references [pg_attribute](catalog-pg-attribute.md).`attnum`) | If a table constraint (including foreign keys, but not constraint triggers), list of the constrained columns |
| `confkey` `int2[]` (references [pg_attribute](catalog-pg-attribute.md).`attnum`) | If a foreign key, list of the referenced columns |
| `conpfeqop` `oid[]` (references [pg_operator](catalog-pg-operator.md).`oid`) | If a foreign key, list of the equality operators for PK = FK comparisons |
| `conppeqop` `oid[]` (references [pg_operator](catalog-pg-operator.md).`oid`) | If a foreign key, list of the equality operators for PK = PK comparisons |
| `conffeqop` `oid[]` (references [pg_operator](catalog-pg-operator.md).`oid`) | If a foreign key, list of the equality operators for FK = FK comparisons |
| `confdelsetcols` `int2[]` (references [pg_attribute](catalog-pg-attribute.md).`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](catalog-pg-operator.md).`oid`) | If an exclusion constraint or `WITHOUT OVERLAPS` primary key/unique 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](catalog-pg-index.md).`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.