sql - Order of ANDS in Where clause for greatest performance

Question

My thinking is that if I put my ANDs that filter out a greater number of rows before those that filter out just a few, my query should run quicker since that selection set is much smaller between And statements.

But does the order of AND in the WHERE clause of an SQL Statement really effect the performance of the SQL that much or are the engines optimized already for this?

Answer 1

It really depends on the optimiser.

It shouldn't matter because it's the optimiser's job to figure out the optimal way to run your query regardless of how you describe it.

In practice, no optimiser is perfect so you might find that re-ordering the clauses does make a difference to particular queries. The only way to know for sure is to test it yourself with your own schema, data etc.