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Types of dependencies

This topic contains short descriptions for each type of database object dependencies.



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 this case the dependent object is dropped as well. Example: a table column has a normal dependency on its data type.



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 auto dependent on the table, so that it will go away if the table is dropped.



The dependent object has been created as a 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.



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



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