mysql 多条数据合并成一条数据

SELECT
dormnum,
floorid,
-- ( select position1 FROM ab where assettypes=0) as a1 ,
-- ( SELECT position2 FROM ab where assettypes=0) as a2 ,
-- ( SELECT position1 FROM ab where assettypes=1) as b1,
-- ( SELECT position2 FROM ab where assettypes=1) as b2
GROUP_CONCAT(position1) as a1,
GROUP_CONCAT(position2) as a2
FROM
ab t
GROUP BY
dormnum