在ORACLE中用A表中的某几列去更新B表的某几列（B表的这几列都不允许为空），如果B表中的记录数超过A表的记录数，按照如下UPDATE语句运行时ORACLE产生如下错误：无法将B表的列更新为NULL，是否在ORACLE中使用子查询进行UPDATE时B表的数量不能超过A表？
update B
set
(serv_id, product_id )=
(select serv_id, product_id
from A where khdjls = B.khdjls and zxxh = B.zxxh
);
update B
set
(serv_id, product_id )=
(select serv_id, product_id
from A where khdjls = B.khdjls and zxxh = B.zxxh
);
set
(serv_id, product_id )=
(select serv_id, product_id
from A where khdjls = B.khdjls and zxxh = B.zxxh
) where exists select 1 from A where A.khdjls = B.khdjls and A.zxxh = B.zxxh你那句的意思除了更新相同的记录外，还将B表中存在的，A表中不存在的主键的行全部置成空
select id,name from a;
id , name
1 aaa
2 bbb
3 cccselect id,name from b;
1 aa
2 bb
3 cc
4 ddupdate b set name = (select name from a where a.id = b.id);执行后
select id, name from b;
1 aaa
2 bbb
3 ccc
4
你可以自己去试试看你这种更新最好是这么写，如果khdjls 和 zxxh 存在联合主键的话
update (select a.serv_id serv_idA, a.product_id product_idA,b.serv_id serv_idB, b.product_id product_idB from A ,B where a.khdjls = B.khdjls and A.zxxh = B.zxxh ) set serv_idB,product_idB = serv_idA,product_idA;