DB2用一张表更新其他表的数据

表结构：
CREATE TABLE ATEST
 (ID    INTEGER,
  NAME  VARCHAR(256),
  CODE  INTEGER,
  NAME2 VARCHAR(256)
 )

CREATE TABLE BTEST
 (ID    INTEGER,
  CODE  INTEGER
 )

CREATE TABLE CTEST
 (ID    INTEGER,
  NAME  VARCHAR(256),
  NAME2 VARCHAR(256)
 )

SQL语句：
一张表更新另一张表的字段：
update atest
set atest.name=(select ctest.name from ctest where atest.id = ctest.id)
where atest.id in  (select ctest.id from ctest);

两张表关联更新另一张表的字段：
update atest
set (name,name2) = (SELECT CASE WHEN CTEST.NAME IS NULL THEN ATEST.NAME ELSE CTEST.NAME END, CASE WHEN CTEST.NAME2 IS NULL THEN ATEST.NAME2 ELSE CTEST.NAME2 END FROM BTEST LEFT JOIN CTEST on BTEST.ID = CTEST.ID  WHERE atest.CODE = BTEST.CODE)
WHERE atest.CODE IN (SELECT BTEST.CODE FROM BTEST);


另外一个: http://blog.csdn.net/Bobwu/archive/2009/01/13/3768636.aspx
1.
declare
cursor t1 is select * from tablename;
begin
for rec in t1 loop
update tablename t set t.detail=rec.jieshao where t.objectid=rec.objid;
end loop;
end; 

2.

update   student   set   (name,id   )=   
  (select   name   ,id     from   (select   student.rowid   rd,student1.name,student1.id   from   student1,student   where   student1.int_id   =student.int_id)   tmp   
  where   student.rowid=tmp.rd);   
  commit; 

3.

update test_a a set (a.name,a.age)=
(select b.name,b.age from test_b b where a.id = b.id) where exists
(select * from test_b c where c.id=a.id)

4.

UPDATE   t_A   SET   Djrq=     
  (   
          SELECT   djrq   FROM   t_B   WHERE   t_A.ID   =   T_B.ID     
          WHERE   ROWNUM   =   1     
  )   
  WHERE   t_A.ID   IN     
  (   
          SELECT   ID   FROM   t_B   WHERE   jwh='XX村'   
  ) 

5.

update tbl1 a
   set (a.col1, a.col2) = (select b.col1, b.col2
                              from tbl2 b
                              where a.key = b.key)
   where a.key in(select key from tbl2)

 

 

 

 

MERGE INTO test1 a
  USING all_objects b
    ON (a.object_id = b.object_id)
  WHEN MATCHED THEN
    UPDATE SET a.status = b.status
  WHEN NOT MATCHED THEN
    INSERT (object_id, status)
    VALUES (b.object_id, b.status); 


   update account
      set firstname = (select max( firstname) from account where userid = 'ACID')
    where userid = 'j2ee'


这是一个经典的问题，太多的理论不说了，我直接举个例子吧。

两张表T_USER(用户信息表)，T_NAME_MAP(新老姓名映射表)

T_USER的字段：USER_ID,USER_NAME,USER_INFO；
T_NAME_MAP的字段：USER_ID，NEW_NAME;

具体语句：
UPDATE T_USER A SET A.USER_NAME = (SELECT B.NEW_NAME FROM T_NAME_MAP B WHERE A.USET_ID = B.USER_ID)
WHERE EXISTS (SELECT 1 FROM T_NAME_MAP C WHERE A.USER_ID = C.USER_ID );

特别提醒：
1、如果T_USER表中的一个USER_ID在T_NAME_MAP 表中存在两条以上的记录，则该语句会报错。因为Oracle是无法辨别你要“更新”哪一条的。当然，从纯技术的角度来看，这种情况也是可以处理的，你可以在B.NEW_NAME 上加一个函数，如MAX(B.NEW_NAME ).
2、WHERE EXISTS 语句绝对不可以省略，有了这个子句，才能实现“一对一”的批量更新，否则会报错“返回多行”了。

以上，希望可以对你有所帮助，共同提高