PostgreSQL 7.4beta4 Documentation
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# 44.13. `pg_depend`

The catalog `pg_depend` records the dependency relationships between database objects. This information allows `DROP` commands to find which other objects must be dropped by `DROP CASCADE` or prevent dropping in the `DROP RESTRICT` case.

Table 44-13. `pg_depend` Columns

Name | Type | References | Description
--- | --- | --- | ---
`classid` | `oid` | `pg_class`.oid | The OID of the system catalog the dependent object is in
`objid` | `oid` | any OID column | The OID of the specific dependent object
`objsubid` | `int4` |  | For a table column, this is the column number (the `objid` and `classid` refer to the table itself). For all other object types, this column is zero.
`refclassid` | `oid` | `pg_class`.oid | The OID of the system catalog the referenced object is in
`refobjid` | `oid` | any oid attribute | The OID of the specific referenced object
`refobjsubid` | `int4` |  | For a table column, this is the column number (the `refobjid` and `refclassid` refer to the table itself). For all other object types, this column is zero.
`deptype` | `char` |  | A code defining the specific semantics of this dependency relationship; see text.

In all cases, a `pg_depend` entry indicates that the referenced object may not be dropped without also dropping the dependent object. However, there are several subflavors identified by `deptype`:

`DEPENDENCY_NORMAL` (n)

  A normal relationship between separately-created objects. The dependent object may be dropped without affecting the referenced object. The referenced object may only be dropped by specifying CASCADE, in which case the dependent object is dropped, too. Example: a table column has a normal dependency on its data type.

`DEPENDENCY_AUTO` (a)

  The dependent object can be dropped separately from the referenced object, and should be automatically dropped (regardless of RESTRICT or CASCADE mode) if the referenced object is dropped. Example: a named constraint on a table is made autodependent on the table, so that it will go away if the table is dropped.

`DEPENDENCY_INTERNAL` (i)

  The dependent object was created as part of creation of the referenced object, and is really just a part of its internal implementation. A `DROP` of the dependent object will be disallowed outright (we'll tell the user to issue a `DROP` against the referenced object, instead). A `DROP` of the referenced object will be propagated through to drop the dependent object whether `CASCADE` is specified or not. Example: a trigger that's created to enforce a foreign-key constraint is made internally dependent on the constraint's `pg_constraint` entry.

`DEPENDENCY_PIN` (p)

  There is no dependent object; this type of entry is a signal that the system itself depends on the referenced object, and so that object must never be deleted. Entries of this type are created only by `initdb`. The columns for the dependent object contain zeroes.

Other dependency flavors may be needed in future.

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