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Using Object IDs (OIDs) in Oracle

Oracle Tips by Mike Ault

Use Of The Dangling Clause

The DANGLING clause is used to test for a dangling REF. In some situations if the application is not coded properly a REFed value could be deleted without removing the REF value in a dependent table. If this deletion of a master object instance without removal of the dependent REF value occurs, the REF value left in the dependent table is said to be DANGLING and an result in problems for retrieves, updates and deletes. An example of the use of this clause would be to set all dangling REF values to null via an update statement such as:


So unless you are absolutely sure that you have no dangling ref values you should use the DANGLING clause to ensure that the records you retrieve are complete. The clause can be used with both IS and IS NOT:

SELECT ename, enumber, DEFRE(edept) FROM emp WHERE edept IS NOT DANGLING;

Always be sure that a REF value is not null before attempting to REF or DEREF it or your session may be terminated (indeed, after several experiments along this line in 8.0.2 Oracle caused my NT4.0 box to reboot) the only way to do this is to use the DANGLING clause.


If you like Oracle tuning, you may enjoy the book Oracle Tuning: The Definitive Reference , with over 900 pages of BC's favorite tuning tips & scripts. 

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