On Delete Restrict or On Delete No Action Tips

Oracle Tips by Burleson Consulting

Question:

Does Oracle 9i or later support On delete Restrict or On delete No action option while creating foreign key?

For example

ALTER TABLE SAMPLE1 ADD FOREIGN KEY (COL1) REFERENCES SAMPLE (COL2)ON DELETE No Action ;

ALTER TABLE SAMPLE1 ADD FOREIGN KEY (COL1) REFERENCES SAMPLE (COL2)ON DELETE RESTRICT ;

Answer:

Oracle allows three different definitions under the definition of the foreign key:

ON DELETE CASCADE (when a referenced parent table row is removed all the child are removed automatically)

The ON DELETE SET NULL action allows data that references the parent key to be deleted, but not updated. When referenced data in the parent key is deleted, all rows in the child table that depend on those parent key values have their foreign keys set to null.

ON DELETE NO ACTION (which is the default) prevents deleting a parent when there are children (would be nice arrangement for real life)

Other referential actions not supported by FOREIGN KEY integrity constraints of Oracle can be enforced using database triggers.

Additional information on ON DELETE can be found HERE.

Comments:

The author suggests that the default or NO ACTION would be a good set up for life. While I understand that it would be nice if young children didn't lose their parents, I think it is possible to look at that statement and say that a parent can't die until he has no children. I believe that no parent should have to bury their child, so perhaps the author didn't look into the statement enough.

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