DANGLING REFs:

When a REF value points to a non-existent object, the REF is said to be DANGLING. A DANGLING is different from being NULL. That is since it is possible for the object identified through a REF to become unavailable - either by deletion of the object or modify in privileges.  Like a REF is called DANGLING REF. To look to see if a REF is dangling or not, An Oracle SQL gives the predicate IS [NOT] DANGLING.

Example

A Record in the table deptab is deleted. If any records are additional referred, dangling can be checked.

INSERT INTO EMPLOYEES SELECT 'Sriram',REF(X) FROM DEPTAB X WHERE depno=20;

1 row created.

DELETE FROM deptab where depno=20;

SELECT k.ename, k.deptinf.dname

FROM EMPLOYEES k WHERE k.DEPTinf IS NOT DANGLING;

ENAME          DEPTINF.DNAME

--------------------  --------------------

Sriram                          Purchase