左连接的表中有多条数据只取一条

取日期最大的一条数据

CREATE   TABLE   a 

(id  INT )

CREATE   TABLE   B

(cid  INT

,adddate DATETIME)

 

INSERT   INTO   a 

SELECT   1 

UNION

SELECT   2   

 

 

INSERT   INTO   b  SELECT   1, '2010-10-01'

UNION   SELECT   1, '2010-10-02'

UNION   SELECT   2, '2010-10-01'

UNION   SELECT   2, '2010-10-02'

UNION   SELECT   2, '2010-10-03'

 

SELECT   *  FROM   a

LEFT   JOIN   ( SELECT   MAX (adddate) AS  adddate ,cid  FROM  b  GROUP   BY  cid ) b1

ON   b1.cid = a.id