Necessity of FOREIGN KEY

Ask question on - DataBase Concepts, IBM Mainframe DB2, DB2/UDB, DB2 Tools, SQL , DB2 programming with languages like COBOL, PL1.

Moderators: Kalicharan, Moderator Group

Post Reply
Posts: 15
Joined: Mon Mar 29, 2010 2:19 pm
Location: India

Necessity of FOREIGN KEY

Post by Aashiq » Thu Mar 29, 2012 4:00 am


Could some one please explain the importance of foreign key?

I have learnt that foreign key is a key from dependent table which is derived from a primary key of the parent table and most importantly foreign key allows duplicates.

For ex: If a parent table EMPLOYEE has a primary key EMPNO


and Dependent table PRJ has a foreign key RESPEMP



now if I want to update the empno - 30 of the parent table EMPLOYEE as 80

But since the value 30 already occurred in the dependent table PRJ it is not allowing me to update the value in Parent table EMPLOYEE. how could I resolve this?

and at the same time I cant delete the same empno 30 from the parent table EMPLOYEE, since the value 30 occurred in the dependent table PRJ.
How could I resolve this.

Thanks for your help in advance.
Last edited by Aashiq on Thu Mar 29, 2012 10:25 pm, edited 1 time in total.
"Helping hand is better than praying lips"

Posts: 15
Joined: Mon Mar 29, 2010 2:19 pm
Location: India

Post by Aashiq » Thu Mar 29, 2012 10:21 pm

Can some one please take a look into this and please give me your inputs..

That would be greatly helpful for me
"Helping hand is better than praying lips"

User avatar
Posts: 981
Joined: Mon Oct 02, 2006 8:31 pm

Post by dbzTHEdinosauer » Fri Mar 30, 2012 1:51 am

have you tried inserting new 80's based on the 30"s in parent table,
then update the 30" in the child to 80's,
delete the 30's from the parent.
Dick Brenholtz
JCL, SQL and code in programs have an irritating habit of doing what you say,
not what you meant.

Post Reply


Free tutorials from mainframegurukul
  • JCL Tutorial
    Covers all important JCL concepts.
  • Cobol Tutorial
    This tutorials covers all Cobol Topics from STRING to COMP-3.
  • DB2 Tutorial
    DB2 Tutorial focuses on DB2 COBOL Programming.
  • SORT Tutorial
    This Tutorial covers all important aspects of DFSORT with examples
  • CICS Tutorial
    This CICS tutorial covers CICS concepts and CICS Basics, CICS COBOL Programming.
Mainframe Interview questions

Other References
Mainframe Tools and others