数据库 a表左连接b表，a中一条数据对应b中多条数据,如何只取b表中createDate最大的一条

CREATE  TABLE  a
(id  INT )
CREATE  TABLE  B
(cid  INT
,createDate DATETIME)

INSERT  INTO  a
SELECT  1
UNION
SELECT  2


INSERT  INTO  b  SELECT  1, '2016-02-19'
UNION  SELECT  1, '2016-02-18'
UNION  SELECT  2, '2016-02-17'
UNION  SELECT  2, '2016-02-16'
UNION  SELECT  2, '2016-02-15'

SELECT  *  FROM  a
LEFT  JOIN  ( SELECT  MAX (createDate) AS  createDate,cid  FROM  b  GROUP  BY  cid) b1
ON  b1.cid = a.id