zoradit, limitovat, opet zoradit, ale podla niecoho ineho

takze majme tabulku napriklad spoluziaci. nech tam budu polia popularita, a vek.

chcem vybrat 5 najpopularnejsich ziakov, avsak vystup chcem zoradit podla veku. teda chcem podla veku zoradenych 5 najpopularnejsich ziakov.

skusal som subrequest, nieco ako select (select meno, vek, popularita from spoluziaci order by popularita limit 5) order by vek, lenze to skoncilo chybou.

neviete, ako by sa to dalo urobit?

Taps: to je blbost, on by ho zoradi podla popularity, ale co dalej?

Kajman_: to vyzera dobre, ale naco je tam slovo tmp ?

btw toto funguje:

select * from (select meno, vek, popularita from spoluziaci order by popularita limit 5) as spoluziaci order by vek

edit: uz chapem to tmp, to si chcel dat as tmp, vsak?

tiso: kym som pisal prispevok, tak si ma predbehol

takto to nefunguje, pretoze ja chcem nieco ine..

to co si napisal urobi asi to, ze zoradi podla popularity, a ak maju nahodou niektori dvaja rovnaku popularitu, tak zoradi podla veku.

ibaze ja chcem 5 najpopularnejsich ziakov, a tych chcem zoradit podla veku..

prikladam vypis

mysql> select * from ziaci; --iba vypis

+------+------------+

| vek  | popularita |

+------+------------+

|    1 |         50 |

|    2 |        100 |

|    3 |         75 |

|    4 |          1 |

|    5 |          2 |

|    6 |         16 |

|    7 |          4 |

+------+------------+

7 rows in set (0.02 sec)



mysql> select * from ziaci order by popularita desc; --zoradit podla popularity

+------+------------+

| vek  | popularita |

+------+------------+

|    2 |        100 |

|    3 |         75 |

|    1 |         50 |

|    6 |         16 |

|    7 |          4 |

|    5 |          2 |

|    4 |          1 |

+------+------------+

7 rows in set (0.00 sec)



mysql> select * from ziaci order by popularita desc limit 3; --troch najpopularnejsich

+------+------------+

| vek  | popularita |

+------+------------+

|    2 |        100 |

|    3 |         75 |

|    1 |         50 |

+------+------------+

3 rows in set (0.00 sec)



mysql> select * from ziaci order by popularita desc, vek desc limit 3; -- a tu je ten tvoj postup. vidis, ze to takto nejde, pretoze nie su zoradeni podla veku

+------+------------+

| vek  | popularita |

+------+------------+

|    2 |        100 |

|    3 |         75 |

|    1 |         50 |

+------+------------+

3 rows in set (0.00 sec)

inac tento priklad zo ziakmi je cisto fiktivny, v skutocnosti riesim nieco ine :) ale na demonstraciu problemu je to dobre..


kazdopadne som sa naucil nieco o subqueries, asi to, ze ked subquery vracia jeden stlpec, tak sa odpoved sprava ako stlpec, teda ju mozeme jednoducho selectnut, a ak subquery vracia viacej stlpcov, tak sa to uz sprava ako tabulka. zaujimave :)