SQL question: Does the order of the WHERE clause make a difference?

Question

From a performance standpoint, does the order of my SQL WHERE statements make a difference?

For instance

SELECT ... FROM ...
WHERE a > 1
AND b <         


        

Answer 1

No, it doesn't. Most modern SQL servers include a query optimizer which looks into all the plausible (*) ways of resolving a query and whereby older servers may take hints based on the order within the SELECT clause, newer servers do not.

The order of the JOINs on the other hand still matter to a greater extent.

Edit: Do see Jonathan's Leffler's response for he provides additional detail in particular regarding the order of JOINs. Thanks you, Jonathan!

Edit: ( * ) Plausible vs. Possible: As pointed out by Erikkalen, the optimizer does not look into all of the possible ways, thanks to [pretty good] heuristics coded in its logic, it will only evaluate the plausible plans, on the basis of the statistics it keeps for the underlying indexes. For each of the plans it considers an overall cost is estimated (or partially so, when partial costs readily exceed the overall cost of another plan [pruning]), and that's how the plan effectively used is eventually selected. While the general principles used by SQL query optimizers are well known, the intricacies of their implementation introduce many different twists-and-turns.