一個Mysql查詢

今天在查詢一個表時,用下面的語句
select distinct concat(slipno,'|',date_format(ydate,'%Y-%m-%d')) as code,slipno as name from bus_cchecks;
結果是:

code	name
o080414001\|200	o080414001

如果將distinct去掉,結果正常,但會重復

後來改用下面的語句
select concat(slipno,'|',date_format(ydate,'%Y-%m-%d')) as code,slipno as name from bus_cchecks group by slipno,ydate;
結果正常:

code	name
o080414001\|2008-04-15	o080414001