From: Rik Wasmus
Date: October 11 2011 1:08pm
Subject: Re: Index question
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Message-Id: <201110111508.52986.rik@grib.nl>
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> In this instance would you create four indexes key(a) key(b) key(a,b) key
> (b,a) ? Or is the decision based on the query response time ?

Depends on the data and usage, but probably I'd go for a index(a,b) & 
index(b,a) if reads heavily outnumber writes.  As index(a) is covered by 
index(a,b), and index(b) by index(b,a), we don't need to add those, which 
saves time on modifications.
-- 
Rik Wasmus