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

It depends on the DBMS. SQL itself does not say anything about how a query should execute. It is up to the specific implementation.

If your DBMS had the very simplistic model of interpreting the query sequentially, then putting a > 1 first in your example would (obviously) be faster - because the DBMS would make two passes of which the second pass is through a much smaller resultset.