Grant Fritchey (11/30/2012)
And the indexes have to be selective enough to be useful for a seek or you'll get scans. Same things apply to non-clustered indexes too.
For lots more detail on query tuning and execution plans, take a look at my books (listed below).
Not for clustered indexes. SQL can do a seek on a clustered index even if you're SELECTing 99% of the rows.
SQL DBA,SQL Server MVP(07, 08, 09)[size=2]Prosecutor James Blackburn, in closing argument in the Fatal Vision murders trial: If in the future, you should cry a tear, cry one for them [the murder victims]. If in the future, you should say a prayer, say one for them. And if in the future, you should light a candle, light one for them.[/size]