I have programs that will utilize index I. I also have programs that will utilize index J. Can I combine the the two indexes into like the example index K below (and both pograms be happy)?

Index I:
Column A
Column B

Index J:
Column A
Column C

Index K:
Column A
Column B
Column C

Thanks,

CougarTrace

Index I is redundant based on the existence of index K.

Index J should be turned around to be:
Column C
Column A

But it is possible that index J is also redundant if the cardinality of Column A is high enough on index K.

I'd not advice to combine the two indices.

If you have a WHERE-Clause like:
WHERE A = .... AND C = ....
the "new" index K has only 1 matching column ( instead of 2, which Index J has ) and that will result in more get-page-requests and a poorer performance.

Programs that use Index I ( with a WHERE-CLause :
WHERE A = ... AND B = .... )
wouldn't be happy too. The additional column might require to read more index-pages.


What would benefit from the combination ?
- each insert / delete / update - as only one index has to be updated
- a SELECT c FROM ... WHERE a = ... AND b = ... - as the query is index-only