Which SQL statement is faster? (HAVING vs. WHERE…)

Question

SELECT NR_DZIALU, COUNT (NR_DZIALU) AS LICZ_PRAC_DZIALU
    FROM  PRACOWNICY
    GROUP BY NR_DZIALU
    HAVING NR_DZIALU = 30

or

SE         


        

Answer 1

It might depend on the engine. MySQL for example, applies HAVING almost last in the chain, meaning there is almost no room for optimization. From the manual:

The HAVING clause is applied nearly last, just before items are sent to the client, with no optimization. (LIMIT is applied after HAVING.)

I believe this behavior is the same in most SQL database engines, but I can't guarantee it.