sql 更新问题

Question

dm  mc  ssdm ssmc 
01  a  
02  b 
03  c  01 
04  d  02 
05  e  03 表如上。所属名称（ssmc）这个字段为空 ，现在想通过一条sql语句更新ssmc字段 
实现的效果如下： 
dm  mc  ssdm ssmc 
01  a  
02  b 
03  c  01  a 
04  d  02  b 
05  e  03  c 

Answer 1

update t
set ssmc = (
select mc
from t t2
where 
t.dm = t2.ssdm
);
try 一下。

Answer 2

update t5
set ssmc=(
select t2.val1
from t5 t2
where t2.dm=t5.ssdm
);

Answer 3

update t5
set ssmc=(
select t2.mc
from t5 t2
where t2.dm=t5.ssdm
);

Answer 4

update ta a set
ssmc=(select mc from ta b where a.dm=b.ssdm)
where exists(select 1 from ta b where a.dm=b.ssdm)

Answer 5

要加where条件，否则没有匹配的也被更新了

Answer 6

dm  mc  ssdm ssmc 
01  a  
02  b 
03  c  01 
04  d  02 
05  e  03 表如上。所属名称（ssmc）这个字段为空 ，现在想通过一条sql语句更新ssmc字段 
实现的效果如下： 
dm  mc  ssdm ssmc 
01  a  
02  b 
03  c  01  a 
04  d  02  b 
05  e  03  c 他表中的ssmc本来就是空的，应该不存在楼上说的那个问题。

Answer 7

SQL> 
SQL> select tab1.dm, tab1.dc, tab1.ssdm, tab2.dc
  2    from csdn_test tab1, csdn_test tab2
  3   where tab1.ssdm = tab2.dm(+)
  4  ;DM                                                                               DC                                                                               SSDM                                                                             DC
-------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- --------------------------------------------------------------------------------
03                                                                               c                                                                                01                                                                               a
04                                                                               d                                                                                02                                                                               b
05                                                                               e                                                                                03                                                                               c
02                                                                               b                                                                                                                                                                 
01                                                                               a                                                                                                                                                                 SQL>