MySQL Query - alternative - php

Question

My query is too long (3-4s). Any idea's how make this faster?
SELECT u.id AS id_uzytkownika,
u.login,
u.ranga,
u.online_light AS online,
(SELECT MAX(id)
FROM uzytkownicy_zdjecia
WHERE id_uzytkownika = u.id
AND prywatna =0) AS id_fotki,
(SELECT fotka
FROM uzytkownicy_zdjecia
WHERE id = id_fotki) AS fotka ,
(SELECT srednia_ocen
FROM uzytkownicy_zdjecia
WHERE id = id_fotki) AS srednia_ocen,
(SELECT ile_ocen
FROM uzytkownicy_zdjecia
WHERE id = id_fotki) AS ile_ocen
FROM uzytkownicy u
WHERE u.foto =1
AND u.plec = "mezczyzna"
ORDER BY srednia_ocen DESC,
ile_ocen DESC,
id_fotki DESC LIMIT 42

Answer 1

Could you maybe explain your table structure and what this query is about? Since the column names are not in English, most readers will probably have a problem understanding what you are trying to do here...
In general, it looks like you have a LOT of nested SELECTS here to the same table - is there any special reason for that?

Answer 2

Try this:
SELECT u.id AS id_uzytkownika,
u.login,
u.ranga,
u.online_light AS online,
(SELECT MAX(id)
FROM uzytkownicy_zdjecia
WHERE id_uzytkownika = u.id
AND prywatna =0) AS id_fotki,
z.fotka,
z.srednia_ocen,
z.ile_ocen
FROM uzytkownicy u
JOIN uzytkownicy_zdjecia z
ON u.id_fotki = z.id
WHERE u.foto =1
AND u.plec = "mezczyzna"
ORDER BY srednia_ocen DESC,
ile_ocen DESC,
id_fotki DESC LIMIT 42
I've substituted 3 subqueries with a JOIN. The first subquery has a different condition, if you can merge that condition withn others queries you can remove that.
Pay attention You have named id_fokta the result of subquery, but the same name has the primary key of uzytkownicy table

Answer 3

You don't have to query the same table with the same criteria again and again. Replace your sub-selects with a simple join. A LEFT JOIN, if it is possible that no matching record exists.
SELECT
u.id AS id_uzytkownika,
u.login,
u.ranga,
u.online_light AS online,
(
SELECT MAX(id)
FROM uzytkownicy_zdjecia
WHERE id_uzytkownika = u.id
AND prywatna =0
) AS id_fotki,
uz.fotka,
uz.srednia_ocen,
uz.ile_ocen
FROM uzytkownicy u
LEFT JOIN uzytkownicy_zdjecia uz ON uz.id = u.id_fotki
WHERE u.foto = 1
AND u.plec = "mezczyzna"
ORDER BY u.srednia_ocen DESC,
u.ile_ocen DESC,
u.id_fotki DESC LIMIT 42
An alternative way to write the query above is to aggregate first and then join:
SELECT
u.id AS id_uzytkownika,
u.login,
u.ranga,
u.online_light AS online,
uzz.id_fotki,
uz.fotka,
uz.srednia_ocen,
uz.ile_ocen
FROM uzytkownicy u
LEFT JOIN uzytkownicy_zdjecia uz ON uz.id = u.id_fotki
LEFT JOIN
(
SELECT id_uzytkownika, MAX(id) AS id_fotki
FROM uzytkownicy_zdjecia
WHERE prywatna =0
GROUP BY id_uzytkownika
) uzz ON uzz.id_uzytkownika = u.id
WHERE u.foto = 1
AND u.plec = "mezczyzna"
ORDER BY u.srednia_ocen DESC,
u.ile_ocen DESC,
u.id_fotki DESC LIMIT 42
By the way: What is "mezczyzna"? A string? Then this should be single quotes.