What was your coolest SQL optimization, on a slow performing query?

Question

Just speaking to a colleague of mine. He was walking with a hop in his step, on the way to the coffee machine.

I asked him \"what\'s with the \'swarmy\' walk?\", he said

Answer 1

I answered this on a previous question ("Biggest performance improvement you’ve had with the smallest change?"), however, it's such a simple improvement, yet one that is and can be so often overlooked, that it bears repeating:

Indexes!