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;