Får ju problem redan här:
Kod:
select * from TabellB;
+----+-----+------+------------+
| Id | PId | Pris | Datum |
+----+-----+------+------------+
| 1 | 1 | 500 | 2011-12-21 |
| 2 | 2 | 600 | 2011-12-21 |
| 3 | 3 | 1000 | 2011-12-07 |
| 4 | 3 | 1800 | 2011-12-13 |
| 5 | 3 | 1500 | 2011-12-18 |
| 6 | 4 | 320 | 2011-12-01 |
+----+-----+------+------------+
Kod:
mysql> select * from TabellB group by PId;
+----+-----+------+------------+
| Id | PId | Pris | Datum |
+----+-----+------+------------+
| 1 | 1 | 500 | 2011-12-21 |
| 2 | 2 | 600 | 2011-12-21 |
| 3 | 3 | 1000 | 2011-12-07 |
| 6 | 4 | 320 | 2011-12-01 |
+----+-----+------+------------+
Vill att den ska välja det senaste priset för en PId