The Importance Of Index Column Order

Erik Darling shows us how arranging columns in an index can make a huge difference in query performance:

while back I promised I’d write about what allows SQL Server to perform two seeks rather than a seek with a residual predicate.

More recently, a post touched a bit on predicate selectivity in index design, and how missing index requests don’t factor that in when requesting indexes.

This post should tie the two together a bit. Maybe. Hopefully. We’ll see where it goes, eh?

Also apropos: missing index hints return results in alphabetical order, not in selectivity order or what would be best for queries. In other words, just because the green text in SSMS says it’s the index you want doesn’t mean it’s the index you need.

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