表结构

功能

用表B的数据（mc列）更新表A的mc列

SQL Server

update A SET A.mc = b.mc FROM A ,B WHERE  A.bmbh = B.bmbh and A.xmbh = B.xmbh;

Access

update A, B  set A.mc = B.mc where A.bmbh = B.bmbh and A.xmbh = B.xmbh;

或

update A INNER JOIN B ON A.bmbh = B.bmbh AND A.xmbh = B.xmbh SET A.mc = B.mc;