卸下重複行從表DB2中在單個查詢中

Question

我有如下3列的表格：

one | two | three | name 
------------------------------------ 
A1  B1   C1  xyz 
A1  B1   C1  pqr  -> should be deleted 
A1  B1   C1  lmn  -> should be deleted 
A2  B2   C2  abc 
A2  B2   C2  def  -> should be deleted 
A3  B3   C3  ghi 
------------------------------------ 

該表不具有任何主鍵列。我無法控制表格，所以我無法添加任何主鍵列。

如圖所示，我想刪除一列，兩列和三列的組合相同的行。因此，如果A1B1C1發生三次（如上面的例子），另外兩個應該被刪除，只有一個應該停留。

如何通過DB2中的一個查詢來實現此目的？

我的要求是針對單個查詢，因爲我會通過java程序運行它。

Answer 1

（這是假設你是在DB2 for Linux的/ UNIX/Windows的，其他平臺可能略有不同）

DELETE FROM 
    (SELECT ROWNUMBER() OVER (PARTITION BY ONE, TWO, THREE) AS RN 
    FROM SESSION.TEST) AS A 
WHERE RN > 1; 

應該給你，你在找什麼。

該查詢使用OLAP functionROWNUMBER()到每個ONE，TWO，THREE組合內分配一個編號爲每一行。然後，DB2能夠將fullselect（A）引用的行與DELETE statement應從表中刪除的行匹配。爲了能夠使用fullselect作爲刪除子句的目標，它必須符合deletable view的規則（請參閱註釋部分下的「可刪除視圖」）。

下面是一些證據（上LUW 9.7測試）：

DECLARE GLOBAL TEMPORARY TABLE SESSION.TEST (
    one CHAR(2), 
    two CHAR(2), 
    three CHAR(2), 
    name CHAR(3) 
) ON COMMIT PRESERVE ROWS; 

INSERT INTO SESSION.TEST VALUES 
    ('A1', 'B1', 'C1', 'xyz'), 
    ('A1', 'B1', 'C1', 'pqr'), 
    ('A1', 'B1', 'C1', 'lmn'), 
    ('A2', 'B2', 'C2', 'abc'), 
    ('A2', 'B2', 'C2', 'def'), 
    ('A3', 'B3', 'C3', 'ghi'); 

DELETE FROM 
    (SELECT ROWNUMBER() OVER (PARTITION BY ONE, TWO, THREE) AS RN 
    FROM SESSION.TEST) AS A 
WHERE RN > 1; 

SELECT * FROM SESSION.TEST; 

編輯2017年3月2日：

針對艾哈邁德·安華的問題，如果你需要捕獲什麼被刪除，你也可以將刪除與「data change statement」結合起來。在這個例子中，你可以做類似以下，這將使你的「RN」一欄，一個，和：

SELECT * FROM OLD TABLE (
    DELETE FROM 
     (SELECT 
      ROWNUMBER() OVER (PARTITION BY ONE, TWO, THREE) AS RN 
      ,ONE 
      ,TWO 
      ,THREE 
     FROM SESSION.TEST) AS A 
    WHERE RN > 1 
) OLD; 

Answer 2

Please take backup of table before deleting the data 

Delete from table where Name in (select name from table 
group by one,two,three 
having count(*) > 2) 

您可以使用

 DELETE from TABLE Group by one,two,three Having count(*) > 2; 

Answer 3

DELETE FROM Table_Name 
WHERE Table_Name_ID NOT IN (SELECT MAX(Table_Name_ID) 
            FROM Table_Name 
            GROUP BY one , 
              two, 
              three) 

一二threee是你重複列Table_Name_ID是PK

Answer 4

DELETE FROM the_table tt 
WHERE EXISTS (SELECT * 
    FROM the_table ex 
    WHERE ex.one = tt.one 
    AND ex.two = tt.two 
    AND ex.three = tt.three 
    AND ex.zname < tt.zname -- tie-breaker... 
    ); 

注：您的SQL方言可能會有所不同。注2：「名稱」是某些平臺上的保留字。更好地避免它。

Answer 5

這是levenlevi的答案的變化不需要對錶的主鍵（現在不能thow測試語法）

DELETE FROM the_table 
WHERE rid_bit(the_table) NOT IN (SELECT MAX(rid_bit(the_table)) 
            FROM the_table 
            GROUP BY one,two,three) 

我認爲iSeries上不支持rid_bit()，但rrn()保存相同的用途

Answer 6

@a_horse_with_no_name的變體爲iseries回答db2，而不使用group by子句和in子句。它的實際工作

DELETE from the_table a 
where rrn(a) < (
select max(rrn(a)) from the_table b 
where a.one = b.one and a.two = b.two and a.three = b.three 
) 

Answer 7

對於其他使用非常舊版本的DB2 SQL的：這些職位的組合幫助識別和2批發布兩次刪除複本。

SELECT * FROM  LIBRARY.TABLE a 
WHERE a.batch in (115131, 115287) 
AND  EXISTS (SELECT 1 from LIBRARY.TABLE d 
    WHERE d.batch in (115131, 115287) 
    AND a.one = d.one AND a.two = d.two AND a.three = d.three 
    GROUP BY d.one, d.two, d.three 
    HAVING count(*) <> 1) 

    AND RRN(a) > (SELECT MIN(RRN(b)) FROM LIBRARY.TABLE b 
     WHERE b.batch in (115131, 115287) 
     AND a.one = b.one AND a.two = b.two AND a.three = b.three);