TSQL查詢，刪除所有重複的記錄，但一個

Question

可能重複：
delete duplicate records in SQL Server

我有哪些獨特的記錄是由複合鍵表示一個表，如（COL_A， COL_B）。

我已經檢查，證實我有重複行我的表使用以下查詢：

select COL_A, COL_B, COUNT(*) 
from MY_TABLE 
group by COL_A, COL_B 
having count(*) > 1 
order by count(*) desc 

現在，我想刪除所有重複的記錄，但只保留一個。

有人可以請說明如何實現這與2列？

編輯： 假設表只有COL_A和COL_B

Answer 1

1解決方案， 它是靈活的，因爲你可以比COL_A和COL_B添加更多的列：

-- create table with identity filed 
-- using idenity we can decide which row we can delete 
create table MY_TABLE_COPY 
(
    id int identity, 
    COL_A varchar(30), 
    COL_B varchar(30) 
    /* 
    other columns 
    */ 
) 
go 
-- copy data 
insert into MY_TABLE_COPY (COL_A,COL_B/*other columns*/) 
select COL_A, COL_B /*other columns*/ 
from MY_TABLE 
group by COL_A, COL_B 
having count(*) > 1 
-- delete data from MY_TABLE 
-- only duplicates (!) 
delete MY_TABLE 
from MY_TABLE_COPY c, MY_TABLE t 
where c.COL_A=t.COL_A 
and c.COL_B=t.COL_B 
go 
-- copy data without duplicates 
insert into MY_TABLE (COL_A, COL_B /*other columns*/) 
select t.COL_A, t.COL_B /*other columns*/ 
from MY_TABLE_COPY t 
where t.id = (
       select max(id) 
       from MY_TABLE_COPY c 
       where t.COL_A = c.COL_A 
       and t.COL_B = c.COL_B 
      ) 
go 

第二個解決方案 如果你真的有兩個col在MY_TABLE UMNS你可以使用：

-- create table and copy data 
select distinct COL_A, COL_B 
into MY_TABLE_COPY 
from MY_TABLE 
-- delete data from MY_TABLE 
-- only duplicates (!) 
delete MY_TABLE 
from MY_TABLE_COPY c, MY_TABLE t 
where c.COL_A=t.COL_A 
and c.COL_B=t.COL_B 
go 
-- copy data without duplicates 
insert into MY_TABLE 
select t.COL_A, t.COL_B 
from MY_TABLE_COPY t 
go 

Answer 2

嘗試：

-- Copy Current Table 
SELECT * INTO #MY_TABLE_COPY FROM MY_TABLE 

-- Delte all rows from current able 
DELETE FROM MY_TABLE 

-- Insert only unique values, removing your duplicates 
INSERT INTO MY_TABLE 
SELECT DISTINCT * FROM #MY_TABLE_COPY 

-- Remove Temp Table 
DROP TABLE #MY_TABLE_COPY 

只要從MY_TABLE刪除行，當你不打破任何外鍵這應該工作。