每辆车只有一个状态吧Select A.*,IsNull(IsNull(B.状态,C.状态),D.状态) As 状态
from A
Left Join B On A.车牌号=B.车牌号
Left Join C On A.车牌号=C.车牌号
Left Join D On A.车牌号=D.车牌号
from A
Left Join B On A.车牌号=B.车牌号
Left Join C On A.车牌号=C.车牌号
Left Join D On A.车牌号=D.车牌号
select * from A
union
select * from B两张合并后,想把某一字段重复的记录保留一条
只能通过把上面上面查询结果当成一个子查询这样去做吗
(select 车牌号,'调动' as zt from B
union all
select 车牌号,'报废' as zt from C
union all
select 车牌号,'转让' as zt from D) AA on A.车牌号=AA.车牌号