a 表id name
------------------------------
1 aa
2 bb
3 cc
4 dd
b 表id a_id date
------------------------------
1 1 7:00
2 1 7:50
3 2 8:10
4 2 8:40
5 1 8:50
6 3 8:00
7 4 9:00
8 3 9:30求列出id name a_id date
------------------------------------
1 aa 1 7:00
2 bb 2 8:10
3 cc 3 8:00
4 dd 4 9:00
------------------------------
1 aa
2 bb
3 cc
4 dd
b 表id a_id date
------------------------------
1 1 7:00
2 1 7:50
3 2 8:10
4 2 8:40
5 1 8:50
6 3 8:00
7 4 9:00
8 3 9:30求列出id name a_id date
------------------------------------
1 aa 1 7:00
2 bb 2 8:10
3 cc 3 8:00
4 dd 4 9:00
from a,(select a_id,min(date) date1 from b group by a_id) c
where a.id = c.a_id