Most efficient SQL index to use when where clause contains some ORs

My apologies if this isn't quite the right group to be asking this too,
however I couldn't find a group specifically relating to query/SQL
execution.

I have a query very similar to:
SELECT * FROM XYZ
WHERE A = ? AND (B = ? OR C = ? OR D = ?) ORDER BY E, F

What indexes should I create to make this run efficiently?  The query
optimizer doesn't make any suggestions.  I have a redbook about DB2/400
indexing strategies, but it doesn't mention anything about what to do when
you have ORs in the WHERE clause.

The best results I've had so far was by creating 4 seperate indexes sorted
by A, B, C and D.  This causes the query optimiser to create bitmaps using
the indexes over A, B, C and D, and then combine the 4 bitmaps to
efficiently pick out the correct records, which is great.  But it then
manually sorts the results which kills the performance.

I've tried all sorts of variatons, such as indexes sorted by:
A, B, E, F
A, C, E, F and
A, D, E, F

or

A, B
A, C
A, D
A, E, F

but it never chooses to use any of these indexes and in fact they just make
things worse.  Any suggestions anybody?

BTW, there are many unique values in each of A, B, C and D, so encoded
vector indexes aren't really appropriate.

Thanks in advance for any insight anybody can offer me on this!

Nigel Gay
Computer Patent Annuities.





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