[SQL] MySQL 5.5 - GROUP BY

[Aigor]

Zkusím hodit testovací data..

mysql> select id_disku, model, dtime, cena, id_obchodu, obchod from v_ceny_disku;
+----------+-------------+---------------------+---------+------------+----------------+
| id_disku | model       | dtime               | cena    | id_obchodu | obchod         |
+----------+-------------+---------------------+---------+------------+----------------+
|        1 | ST2000DL003 | 2012-05-14 08:24:28 | 2734.00 |          1 | AlfaComp       |
|        1 | ST2000DL003 | 2012-04-13 09:55:55 | 2799.00 |          1 | AlfaComp       |
|        1 | ST2000DL003 | 2012-03-15 09:56:44 | 2820.00 |          1 | AlfaComp       |
|        1 | ST2000DL003 | 2012-03-01 09:57:54 | 2797.00 |          1 | AlfaComp       |
|        1 | ST2000DL003 | 2012-01-30 09:58:15 | 3341.00 |          1 | AlfaComp       |
|        2 | WD20EARX    | 2012-01-30 10:05:55 | 3100.00 |          1 | AlfaComp       |
|        2 | WD20EARX    | 2012-03-01 10:06:12 | 3060.00 |          1 | AlfaComp       |
|        2 | WD20EARX    | 2012-03-15 10:06:37 | 2840.00 |          1 | AlfaComp       |
|        2 | WD20EARX    | 2012-04-13 10:06:49 | 2720.00 |          1 | AlfaComp       |
|        2 | WD20EARX    | 2012-05-14 10:07:43 | 2700.00 |          1 | AlfaComp       |
|        3 | WD30EZRX    | 2012-01-30 10:09:53 | 4277.00 |          1 | AlfaComp       |
|        3 | WD30EZRX    | 2012-03-01 10:10:11 | 4011.00 |          1 | AlfaComp       |
|        3 | WD30EZRX    | 2012-03-15 10:10:39 | 4059.00 |          1 | AlfaComp       |
|        3 | WD30EZRX    | 2012-04-13 10:10:49 | 3820.00 |          1 | AlfaComp       |
|        3 | WD30EZRX    | 2012-05-14 10:11:08 | 3813.00 |          1 | AlfaComp       |
|        3 | WD30EZRX    | 2012-05-14 12:23:26 | 3895.00 |          2 | Czech Computer |
|        3 | WD30EZRX    | 2012-05-14 12:24:10 | 4055.00 |          3 | Alza           |
|        3 | WD30EZRX    | 2012-05-14 12:24:10 | 3907.00 |          4 | Softcom        |
+----------+-------------+---------------------+---------+------------+----------------+

A výsledek dotazu

mysql> SELECT serie, model, MAX(dtime) as max_datum, cena, obchod FROM v_ceny_disku GROUP BY model,obchod;
+-------------------------+-------------+---------------------+---------+----------------+
| serie                   | model       | max_datum           | cena    | obchod         |
+-------------------------+-------------+---------------------+---------+----------------+
| Seagate Barracuda Green | ST2000DL003 | 2012-05-14 08:24:28 | 2734.00 | AlfaComp       |
| WD Caviar Green         | WD20EARX    | 2012-05-14 10:07:43 | 3100.00 | AlfaComp       |
| WD Caviar Green         | WD30EZRX    | 2012-05-14 10:11:08 | 4277.00 | AlfaComp       |
| WD Caviar Green         | WD30EZRX    | 2012-05-14 12:24:10 | 4055.00 | Alza           |
| WD Caviar Green         | WD30EZRX    | 2012-05-14 12:23:26 | 3895.00 | Czech Computer |
| WD Caviar Green         | WD30EZRX    | 2012-05-14 12:24:10 | 3907.00 | Softcom        |
+-------------------------+-------------+---------------------+---------+----------------+
6 rows in set (0.00 sec)

Viditelně např. cena WD20EARX je špatně, datum sice mělo by to vracet 2700,-
Stejně tak u WD30EZRX je chybně cena 4277,-

Vážně nechápu...