Oracle执行Update语句的几种方式

update  a 
set a.c2= (select b.c2from  b where a.c1=b.c1)
where exists   (select 1 from   b where a.c1=b.c1)

update (select a.c2 as ac2,b.c2 as bc2 from a, b where a.c1=b.c1 and a.c3='2011') as M 
set ac2=bc2

MERGE INTO table_name alias1 --主表，即需要被修改的表
USING (table | view | sub_query) alias2 --从表，即来源表
ON (join condition) --连接条件
WHEN MATCHED THEN --在匹配的记录中进行
  UPDATE table_name SET col1 = col_val1, col2 = col2_val --更改主表信息
WHEN NOT MATCHED THEN --在不匹配的情况下，筛选从表记录插入到主表【可选】
  INSERT (column_list) VALUES (column_values);

merge into a
using b 
 on (a.c1=b.c1 and a.c3='2011')
   when matched then
update a.c2=b.c2

begin
for cr in (查询语句) loop  --循环
update table_name set ...   --更新语句（根据查询出来的结果集合）
end loop;  --结束循环
end;

begin
    for cur in (select a.rowid  ,b.c2 from  a, b where a.c1=b.c1 and a.c3='2011' )  loop
        UPDATE a  set c2=cur.c2  where rowid=cur.rowid;
    end loop;
end;