What are your most common sql optimizations?

Question

What are your most common SQL optimization that you used?

Answer 1

If you're talking common as in really common then Indexes are the first thing that pops up into my head.

They are a powerful technique that are often misunderstood and quite often abused.

Then I would place de-normalization which can add in quite a bit of performance for many databases.

Query optimization is third and it helps a lot too. I use MySQL these days and Query logging helps a lot for optimization.

Memcached is definitely not common, though caching of some sort is a part of many websites at the scripting end (ASP.Net or PHP).