删除重复记录而不使用公用表表达式（CTE）

Question

我知道如何使用CTE删除重复记录。

如何在不使用CTE [面试问题]的情况下实现这一目标

有可能吗？

示例：包含以下数据的表：

name     salary
-----------------
Husain   20000.00
Husain   20000.00
Husain   20000.00
Munavvar 50000.00
Munavvar 50000.00

删除重复记录后 table应该包含这样的数据：

name     salary
-----------------
Husain   20000.00
Munavvar 50000.00

Answer 1

如果必须删除保留一行此类行的重复行，则可以在SQL中使用ROW_NUMBER（）函数。删除行号＆gt;的所有行1.假设你知道ROW_NUMBER（）和PARTITION是如何工作的。如果没有，你可以在msdn上获得更多相关信息。

DELETE A
FROM
(
SELECT name,salary, ROW_NUMBER() OVER (PARTITION BY name,salary ORDER BY name) AS rn
FROM Tab
) A
WHERE A.rn > 1

只是对@TimSchmelter的回复进行了提醒，它将删除所有重复项的存在。请注意区别，您可以根据自己的要求使用。

Answer 2

使用子查询和GROUP BY HAVING COUNT(*) > 1。

假设您要根据两列col1和col2找到重复项：

查询列出所有重复项：

SELECT t.*
FROM dbo.TableName t
INNER JOIN 
(
   SELECT [col1], [col2], Cnt = COUNT(*)
   FROM dbo.TableName t
   GROUP BY [col1], [col2]
   HAVING COUNT(*) > 1
) Duplicates
ON t.[col1] = Duplicates.[col1] AND t.[col2] = Duplicates.[col2]

删除它们：

DELETE dbo.TableName
FROM dbo.TableName t
INNER JOIN 
(
   SELECT [col1], [col2], Cnt = COUNT(*)
   FROM dbo.TableName t
   GROUP BY [col1], [col2]
   HAVING COUNT(*) > 1
) Duplicates
ON t.[col1] = Duplicates.[col1] AND t.[col2] = Duplicates.[col2]

Answer 3

1. Correlated Subqueries
2. Self Joins

Answer 4

select * from DuplicateRcordTable

WITH CTE 
AS
(
SELECT *,
ROW_NUMBER() OVER(PARTITION BY Col3 ORDER BY Col3) AS DuplicateCount
FROM DuplicateRcordTable
)
DELETE
FROM CTE
WHERE DuplicateCount > 1

select * from DuplicateRcordTable2

Answer 5

Select *  into #temp 

from Emp_Details 

group by Name, Salary

having count(*) =1 

现在，截断原始表

Truncate table Emp_Details 

同样，将记录从临时表插入Emp_Details

insert Emp_Details (Name, Salary, Address)

Select Name, Age, Address from #temp

Answer 6

公用表表达式（CTE）的最常见用法是从没有主键的表中删除重复记录

WITH a as
(
SELECT A,ROW_NUMBER() OVER(PARTITION by A, B ORDER BY A) 
AS duplicateRecCount dbo.A
)
--Now Delete Duplicate Records
DELETE FROM A
WHERE duplicateRecCount > 1 [enter image description here][1]

Answer 7

我们还可以使用光标或使用其他lopping语句从表中删除重复记录。以下代码spinets使用Cursor删除重复记录

  DECLARE @A nvarchar(50), @B nvarchar(50) , @C nvarchar(50), @TotalDuplicate INT ; 



DECLARE a_cursor CURSOR FOR   
SELECT A, B  ,C ,COUNT(1)-1 AS TotalDuplicate
FROM A  
GROUP BY  A, B  ,C 
HAVING COUNT(1)>1

OPEN a_cursor  

FETCH NEXT FROM a_cursor INTO @A, @B,@C,@TotalDuplicate  

WHILE @@FETCH_STATUS = 0  
BEGIN  

    DELETE TOP (@TotalDuplicate) FROM A WHERE A=@A AND B=@B AND C=@C 

    FETCH NEXT FROM a_cursor INTO @A, @B,@C,@TotalDuplicate  

END

CLOSE a_cursor;  
DEALLOCATE a_cursor;