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我有以下代码来检测单个表中的重复项：

      UPDATE tab
        SET dup = 'Y'
      WHERE ROWID IN
        (SELECT tab_o.ROWID
          FROM tab tab_o,
            (SELECT *
             FROM tab tab_i
             WHERE ROWID IN
              (SELECT ROWID
               FROM
                (SELECT ROWID,
                  ROW_NUMBER() OVER(PARTITION BY a, b, c ORDER BY a, b, c) dupl
                 FROM tab
                 WHERE a IS NOT NULL
                   AND a    = 1
                   AND b    = 1
                   AND c    = 3
                )
               WHERE dupl > 1
              )
          ) res
         WHERE tab_o.a  = res.a
          AND tab_o.b   = res.b
          AND tab_o.c   = res.c
        );

我搜索了很多网站，发现大多数人都遵循这种有效的方式。但是我没有找到关于这些嵌套查询如何工作的正确解释。

4

1 回答 1

1

让它更简单。无需分析。

样品表：

12:57:37 SYSTEM@dwal> create table dupe_test
                   2  (a number, b number, c number, is_dupe char);

Table created.                                                                           

12:57:50 SYSTEM@dwal> insert all                    
12:57:50   2    into dupe_test values (1, 1, 1, 'n')
12:57:50   3    into dupe_test values (1, 1, 1, 'n')
12:57:50   4    into dupe_test values (1, 1, 1, 'n')
12:57:50   5    into dupe_test values (1, 2, 1, 'n')
12:57:50   6    into dupe_test values (1, 2, 1, 'n')
12:57:50   7    into dupe_test values (1, 2, 1, 'n')
12:57:50   8  select * from dual;                   

6 rows created.

它是：

12:58:17 SYSTEM@dwal> select * from dupe_test;

         A          B          C I            
---------- ---------- ---------- -            
         1          1          1 n            
         1          1          1 n            
         1          1          1 n            
         1          2          1 n            
         1          2          1 n            
         1          2          1 n            

6 rows selected.

独特的价值观：

12:59:35 SYSTEM@dwal> select rowid,  t.* 
                   2  from dupe_test t 
                   3  where rowid in (select min(rowid) 
                   4                  from dupe_test 
                   5                  group by a, b, c);

ROWID                       A          B          C I                                                                        
------------------ ---------- ---------- ---------- -                                                                        
AAARN1AABAAAO9JAAD          1          2          1 n                                                                        
AAARN1AABAAAO9JAAA          1          1          1 n

更新和结果：

12:59:51 SYSTEM@dwal> update dupe_test t 
                   2  set is_dupe = 'y' 
                   3  where rowid not in (select min(rowid) 
                   4                      from dupe_test 
                   5                      group by a, b, c); 

4 rows updated.                                                                                                                    

13:00:45 SYSTEM@dwal> select * from dupe_test;                                                                                     

         A          B          C I                                                                                                 
---------- ---------- ---------- -                                                                                                 
         1          1          1 n                                                                                                 
         1          1          1 y                                                                                                 
         1          1          1 y                                                                                                 
         1          2          1 n                                                                                                 
         1          2          1 y                                                                                                 
         1          2          1 y                                                                                                 

6 rows selected.

更新：

我想要做的是我发现表中的一个条目在同一个表中重复，所有这些条目都将被标记为 dupl 标志，包括原始条目

仍然不需要分析。只需添加having count(*) = 1您的子查询，因此您将只更新非唯一行。Having子句基本上是聚合函数的 where 条件，无需将查询包装在子查询中。最后执行。

11:03:00 SYSTEM@dwal> insert into dupe_test values (1,3,1,'n') -- add some unique row
11:03:09   2  /                                                                      

1 row created.                                                                       

11:03:10 SYSTEM@dwal> update dupe_test set is_dupe = 'y'                             
11:03:27   2  where rowid not in                                                     
11:03:34   3  (select min(rowid) from dupe_test                                      
11:03:51   4  group by a,b,c                                                         
11:04:00   5  having count(*) = 1);                                                  

6 rows updated.                                                                      

11:04:06 SYSTEM@dwal> select * from dupe_test;                                       

         A          B          C I                                                   
---------- ---------- ---------- -                                                   
         1          1          1 y                                                   
         1          1          1 y                                                   
         1          1          1 y                                                   
         1          2          1 y                                                   
         1          2          1 y                                                   
         1          2          1 y                                                   
         1          3          1 n                                                   

7 rows selected.
于 2012-11-09T05:06:06.620 回答