Question

表A具有这样的数据

JID  P_ID P_CODE   COMM      MDATE
---  ---- ------   ----      ---------
1     112  WXCVA   null      2-feb-19  
1     112  UCXVA   WXCVA     09-sep-19 
2     222  DCVA    null      08-aug-18   
2     222  UCVA    DCVA      09-dec-09

有200条这样的记录。现在，我需要阅读这些记录并更新辅助代码的日期。结果表应该看起来像这样

JID  P_ID P_CODE   COMM      MDATE
---  ---- ------   ----      ---------
1     112  WXCVA   null      2-feb-19  
1     112  UCXVA   WXCVA     2-feb-19 
2     222  DCVA    null      08-aug-18   
2     222  UCVA    DCVA      08-aug-18

如何实现？

Answer 1

create table mytab(p_id number, p_code varchar2(10), comm varchar2(10), mdate date);

insert into mytab values(112, 'WXCVA', null, to_date('20190202','yyyymmdd'));
insert into mytab values(112, 'UCXVA', 'WXCVA', to_date('20190909','yyyymmdd'));
insert into mytab values(222, 'DCVA', null, to_date('20180808','yyyymmdd'));
insert into mytab values(222, 'UCVA', 'DCVA', to_date('20091209','yyyymmdd'));

COMMIT;

select * from mytab;

P_ID P_CODE COMM  MDATE
112  WXCVA  NULL  02-FEB-19
112  UCXVA  WXCVA 09-SEP-19
222  DCVA   NULL  08-AUG-18
222  UCVA   DCVA  09-DEC-09

合并语句以执行所需的更新。

MERGE INTO MYTAB C
USING (SELECT A.P_ID, B.P_CODE, B.COMM, A.MDATE 
         FROM MYTAB A 
              INNER JOIN 
              MYTAB B 
           ON A.P_ID = B.P_ID 
          AND A.P_CODE = B.COMM) D
   ON (   C.P_ID = D.P_ID 
      AND C.P_CODE = D.P_CODE)
 WHEN MATCHED 
 THEN UPDATE SET C.MDATE = D.MDATE;

select * from mytab;

P_ID P_CODE COMM  MDATE
112  WXCVA  NULL  02-FEB-19
112  UCXVA  WXCVA 02-FEB-19
222  DCVA   NULL  08-AUG-18
222  UCVA   DCVA  08-AUG-18

Answer 2

这是您想要的吗？

update tab
   set mdate = (select t2.mdate
                from tab t2
                where t2.p_code = tab.comm
               )
   where tab.comm is not null;

Answer 3

对于您发布的示例数据，此更新声明应该有效：

update tablename t
set t.mdate = (
  select mdate
  from tablename
  where p_id = t.p_id and comm is null
)
where t.comm is not null;

请参见demo。
结果：

P_ID | P_CODE | COMM  | MDATE    
---: | :----- | :---- | :--------
 112 | WXCVA  | null  | 02-FEB-19
 112 | UCXVA  | WXCVA | 02-FEB-19
 222 | DCVA   | null  | 08-AUG-18
 222 | UCVA   | DCVA  | 08-AUG-18

遍历表中的选择查询结果和同一表中的“更新”列

3 个答案: