MYSQL查询问题急求

Question

我现在用的 
SELECT sum( `in` ) `in` , sum( `out` ) `out` , sum( `c2` ) `c2` , `er` FROM `clickip` WHERE `date` = '20120629'为什么得不到这样结果 
id     er       in       out       c2 
30      lun78         2        1         1 
29      baba7         1        0         0 

Answer 1

SELECT sum( `in` ) `in` , sum( `out` ) `out` , sum( `c2` ) `c2` , `er` FROM `clickip` WHERE `date` = '20120629' group by `er`

Answer 2

SELECT `er`,sum( `in` ) `in` , sum( `out` ) `out` , sum( `c2` ) `c2`  FROM `clickip` WHERE `date` = '20120629' group by `er`

Answer 3

SELECT er,max(id),sum( `in` ) `in` , sum( `out` ) `out` , sum( `c2` ) `c2` , `er` FROM `clickip` WHERE `date` = '20120629'
group by er

Answer 4

select id,sum('in') 'in',sum('out')'out',sum('c2')'c2',er
from 'clickip'
where date='20120629'
group by id,er
order by id desc;