Composite primary key

via · Post by **via** » Mon Apr 02, 2007 9:20 am

Hi,
Can a column in a composite primary key be a null? we have a primary key with combination of 2 key columns.In those 2 key columns , can anyone be null?
Database is DB29.Does it accept? Any ideas.

Thanks

ray.wurlod · Post by **ray.wurlod** » Mon Apr 02, 2007 9:21 am

ray.wurlod · Post by **ray.wurlod** » Mon Apr 02, 2007 9:22 am

No.

(having some transmission difficulties here - moderator, please remove)

ray.wurlod · Post by **ray.wurlod** » Mon Apr 02, 2007 9:23 am

All primary key columns in DB2 tables must be NOT NULL.

Re-design the target table. Or use a dedicated default value.

What does it really mean that you want to make part of a key unknown? Ponder on that for a while.

via · Post by **via** » Mon Apr 02, 2007 9:31 am

Thanks Ray..

via · Post by **via** » Mon Apr 02, 2007 10:46 am

Hi,
I got small doubt.If a key is specified on a column, Does it mean that it is indexed as a default? And if we create index on a column, does it mean that its a key?
I appreciate any clarifications..
Thanks

DSguru2B · Post by **DSguru2B** » Mon Apr 02, 2007 10:51 am

No. But usually indices are created on keys for faster updates and retrievals.

The vice versa is also not important, i.e, if an index is set on a column, it does'nt mean it is a key.

via · Post by **via** » Mon Apr 02, 2007 10:59 am

Thanks Brian..But i want to know as key is created on a column, is it indexed as well? or should we explicitly create an index on that key column.

Thanks

DSguru2B · Post by **DSguru2B** » Mon Apr 02, 2007 11:00 am

Indices need to be created explicitly, so yes, create them explicitly.

via · Post by **via** » Mon Apr 02, 2007 11:04 am

Thanks for the clarification..Really this DSXchange is helping a lot..

ray.wurlod · Post by **ray.wurlod** » Mon Apr 02, 2007 11:45 am

Note that the answer given relates to DB2. Some databases do automatically create an index on the primary key (though not on its individual columns).

via · Post by **via** » Tue Apr 03, 2007 3:28 pm

Thanks Ray for pointing that..