MySQL Performance Tuning Have an INDEX
Example
The most important thing for speeding up a query on any non-tiny table is to have a suitable index.
WHERE a = 12 --> INDEX(a)
WHERE a > 12 --> INDEX(a)
WHERE a = 12 AND b > 78 --> INDEX(a,b) is more useful than INDEX(b,a)
WHERE a > 12 AND b > 78 --> INDEX(a) or INDEX(b); no way to handle both ranges
ORDER BY x --> INDEX(x)
ORDER BY x, y --> INDEX(x,y) in that order
ORDER BY x DESC, y ASC --> No index helps - because of mixing ASC and DESC
