PostgreSQL
52.13. pg_constraint
The catalog pg_constraint stores check, 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.) Not-null constraints 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 52.13. pg_constraint Columns
| Name | Type | References | Description |
|---|---|---|---|
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Row identifier (hidden attribute; must be explicitly selected) |
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Constraint name (not necessarily unique!) |
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The OID of the namespace that contains this constraint |
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Is the constraint deferrable? |
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Is the constraint deferred by default? |
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Has the constraint been validated? Currently, can only be false for foreign keys and CHECK constraints |
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The table this constraint is on; 0 if not a table constraint |
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The domain this constraint is on; 0 if not a domain constraint |
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The index supporting this constraint, if it’s a unique, primary key, foreign key, or exclusion constraint; else 0 |
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The corresponding constraint in the parent partitioned table, if this is a constraint in a partition; else 0 |
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If a foreign key, the referenced table; else 0 |
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Foreign key update action code: |
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Foreign key deletion action code: |
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Foreign key match type: |
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This constraint is defined locally for the relation. Note that a constraint can be locally defined and inherited simultaneously. |
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The number of direct inheritance ancestors this constraint has. A constraint with a nonzero number of ancestors cannot be dropped nor renamed. |
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This constraint is defined locally for the relation. It is a non-inheritable constraint. |
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If a table constraint (including foreign keys, but not constraint triggers), list of the constrained columns |
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If a foreign key, list of the referenced columns |
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If a foreign key, list of the equality operators for PK = FK comparisons |
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If a foreign key, list of the equality operators for PK = PK comparisons |
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If a foreign key, list of the equality operators for FK = FK comparisons |
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If an exclusion constraint, list of the per-column exclusion operators |
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If a check constraint, an internal representation of the expression |
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If a check constraint, a human-readable representation of the expression |
+
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
consrc is not updated when referenced objects change; for example, it won’t track renaming of columns. Rather than relying on this field, it’s best to use pg_get_constraintdef() to extract the definition of a check constraint.