Can Multiple Indexes Work Together?

Question

Suppose I have a database table with two fields, \"foo\" and \"bar\". Neither of them are unique, but each of them are indexed. However, rather than being indexed together, th

Answer 1

Eli,

In a comment you wrote:

Unfortunately, I have a table with lots of columns each with their own index. Users can query any combination of fields, so I can't efficiently create indexes on each field combination. But if I did only have two fields needing indexes, I'd completely agree with your suggestion to use two indexes. – Eli Courtwright (Sep 29 at 15:51)

This is actually rather crucial information. Sometimes programmers outsmart themselves when asking questions. They try to distill the question down to the seminal points but quite often over simplify and miss getting the best answer.

This scenario is precisely why bitmap indexes were invented -- to handle the times when unknown groups of columns would be used in a where clause.

Just in case someone says that BMIs are for low cardinality columns only and may not apply to your case. Low is probably not as small as you think. The only real issue is concurrency of DML to the table. Must be single threaded or rare for this to work.