关于查询统计的问题。。紧急紧急啊

Question

测试数据
ID              TIME               VALUE
1            2009-01-01             11
1            2009-02-01             12
1            2009-03-01             13
1            2009-04-01             14
2            2009-05-02             15
2            2009-01-01             16
3            2009-02-01             17
2            2009-03-01             18
2            2009-04-01             19
3            2009-05-02             22
3            2009-05-02             21
3            2009-05-02             23
我现在想按ID号来统计 2009-01-01到2009-05-02 VALUE的平均值（2009-01-01的VALUE 减去 2009-05-02的VALUE）这个语句怎么写啊。

Answer 1

select id,avg(value) 
from table
where time between '2009-01-01' and '2009-05-02'
group by id

Answer 2

select id,avg(value)
from tbname
where time between '2009-01-01' and '2009-05-02'
group by id

Answer 3

晕。。居然忘记AVG函数了。。

Answer 4

select id , avg(value*1.0) avg_value
from tb
where time between '2009-01-01' and '2009-05-02'
grup by id

Answer 5

select id , avg(value*1.0) avg_value
from tb
where time between '2009-01-01' and '2009-05-02'
group by id

Answer 6

（2009-01-01的VALUE 减去 2009-05-02的VALUE）这个是什么。