We can decide which indices we have, you know. The conditions that you state are not by far the only conditions when a multi column index helps you. Even if yo

We can decide which indices we have, you know. The conditions that you state are not by far the only conditions when a multi column index helps you. Even if you do not sort by the index order, and you do not have all the data in the index, the index may still be way more efficient. For example if you have SELECT A WHERE X=3 AND Y=5 ORDER BY B with an index (X,Y).