declare @tyear as int,@tmonth as int
set @tyear=2011
set @tmonth=10
select
 distinct left(convert(varchar,c.checktime,120),10) as mydate,
 u.userid,u.name,
 (select
    substring(CONVERT(varchar, min(checktime), 120 ),12,5) 
  from
    checkinout 
  where
    left(CONVERT(varchar, checktime, 120 ),10)=left(convert(varchar,c.checktime,120),10) 
  and
    userid=u.userid) as mintime,
 (select
    substring(CONVERT(varchar, max(checktime), 120 ),12,5) 
  from
    checkinout where left(CONVERT(varchar, checktime, 120 ),10)=left(convert(varchar,c.checktime,120),10) 
   and userid=u.userid) as maxtime
from
   checkinout as c,userinfo as u 
where
  year(c.checktime)=@tyear 
and
  month(c.checktime)=@tmonth 
order by
   u.userid,mydate

------解决方案--------------------
建议：把子查询放临时表处理，你这里函数用得太多 即使加索引都失效。
不用DISTINCT 改成GROUP BY

------解决方案--------------------
SQL code

--试试是不是这个结果和你的一样不
select u.userid,u.name,
convert(varchar(10),c.checktime,120) as mydate,
CONVERT(varchar(5),min(c.checktime),108) as mintime,
CONVERT(varchar(5),max(c.checktime),108) as mintime
from checkinout c join userinfo u on (c.userid=u.userid) 
where c.checktime>=@tyear+@tmonth+'01' and c.checktime<dateadd(month,1,@tyear+@tmonth+'01')
group by u.userid,u.name,convert(varchar(10),c.checktime,120)
order by 1,3

------解决方案--------------------
select u.userid,u.name,
convert(varchar(10),c.checktime,120) as mydate,
CONVERT(varchar(5),min(c.checktime),108) as mintime,
CONVERT(varchar(5),max(c.checktime),108) as mintime
from checkinout c join userinfo u on (c.userid=u.userid)  
where c.checktime>=@tyear+@tmonth+'01' and c.checktime<dateadd(month,1,@tyear+@tmonth+'01')
group by u.userid,u.name,convert(varchar(10),c.checktime,120)
order by 1,3

看看

------解决方案--------------------
SQL code

declare @tyear as int ,@tmonth as int
select @tyear = 2011,@tmonth = 10

select distinct
        left(convert(varchar, c.checktime, 120), 10) as mydate ,
        u.userid ,
        u.name ,
        ( select    substring(convert(varchar, min(checktime), 120), 12, 5)
          from      checkinout
          where     left(convert(varchar, checktime, 120), 10) = left(convert(varchar, c.checktime, 120),
                                                              10)
                    and userid = u.userid
        ) as mintime ,
        ( select    substring(convert(varchar, max(checktime), 120), 12, 5)
          from      checkinout
          where     left(convert(varchar, checktime, 120), 10) = left(convert(varchar, c.checktime, 120),
                                                              10)
                    and userid = u.userid
        ) as maxtime
from    checkinout as c ,userinfo as u
where   year(c.checktime) = @tyear and month(c.checktime) = @tmonth
order by u.userid ,mydate

/*
left(convert(