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如何防止update语句将某些记录设置为空?

sql-update oracle sql

MoxGoat · 技术社区 · 6 年前

update t1 x
set x.code =
(select code from
(select distinct address, city, prov, aflag, rcode from t2) y
where x.address = y.address and x.city = y.city and x.state = y.state and x.flag = y.flag)
where x.aflag like '%b%';

   t1               
address city    state   flag    code
123      aaa      il     b       400
567      bbb      il     b       400
345      bbb      il     b      -500
789      ddd      il     b       600
546      ccc      il     b       700

表2:用于更新T1的代码列

t2              
address city    state   flag    code
   123   aaa      il      b     -555
   444   bbb      il      b     -555
   345   bbb      il      b     -555
   888   kkk      il      b     -555
   546   ccc      il      b     -555



What the query currently outputs

     current output             
    address city    state   flag    code
       123   aaa      il      b     400
       444   bbb      il      b     NULL
       345   bbb      il      b     -500
       888   kkk      il      b     NULL
       546   ccc      il      b     -700

  What I want               
address city    state   flag    code
  123    aaa      il      b     400
  444    bbb      il      b    -555
  345    bbb      il      b    -500
  888    kkk      il      b    -555
  546    ccc      il      b    -700

3 回复 | 直到 6 年前

Gordon Linoff 6 年前

exists where

update t1 x
    set x.code = (select code
                  from t2 y
                  where x.address = y.address and x.city = y.city and x.state = y.state and x.flag = y.flag and rownum = 1
                 )
    where x.aflag like '%b%' and
          exists (select code
                  from t2 y
                  where x.address = y.address and x.city = y.city and x.state = y.state and x.flag = y.flag and rownum = 1
                 );

Thorsten Kettner 6 年前

t2 都应告诉您要更新的行和使用的值。为此,请编写一个updatetable查询:

update
(
  select t1.code, t2.code as new_code
  from t1
  join t2 on  t2.address = t1.address
          and t2.city    = t1.city city 
          and t2.state   = t1.state
          and t2.flag    = t1.flag
  where t1.flag like '%b%'
)
set code = new_code;

address, city, state, flag

wolÏi 6 年前

有些人喜欢它,有些人不喜欢。它看起来与您最初的更新声明惊人地相似:

MERGE INTO t1 x
USING (SELECT DISTINCT address, city, state, flag, code from t2) y
   ON (x.address = y.address AND x.city = y.city AND x.state = y.state AND x.flag = y.flag)
 WHEN MATCHED THEN 
      UPDATE SET x.code = y.code
       WHERE x.flag LIKE '%b%';

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