mysql如何實作查重只留一個

mysql實現查重只留一個的方法：首先透過「select * from」查找表中多餘的重複記錄；然後透過「delete from」刪除重複數據，並只保留一個資料。

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mysql 刪除重複資料只保留一筆記錄

刪除重複資料保留name中id最小的記錄

delete from order_info where id not in (select id from (select min(id) as id from order_info group by order_number) as b);

delete from table where id not in (select min(id) from table group by name having count(name)>1) and  id in (select id group by name having count(name)>1)

(注意：HAVING 子句對GROUP BY 子句設定條件的方式與WHERE 和SELECT 的交互方式類似。WHERE搜尋條件在進行分組操作之前應用；而HAVING 搜尋條件在進行分組操作之後應用。HAVING 語法與WHERE 語法類似，但HAVING 可以包含聚合函數。HAVING 子句可以引用選擇清單中顯示的任意項。)

擴充：

SQL：刪除重複數據，只保留一條用SQL語句,刪除重複項只保留一條在幾千筆記錄裡,存在著些相同的記錄,如何能用SQL語句,刪除掉重複的呢

 1、查找表中多餘的重複記錄，重複記錄是根據單一字段（peopleId）來判斷

select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)

2、刪除表中多餘的重複記錄，重複記錄是根據單一欄位（peopleId）來判斷，只留有rowid最小的記錄 

delete from people where   peopleName in (select peopleName    from people group by peopleName      having count(peopleName) > 1) and   peopleId not in (select min(peopleId) from people group by peopleName     having count(peopleName)>1)

3、查找表中多餘的重複記錄（多個欄位）

select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)

4、刪除表中多餘的重複記錄（多個欄位），只留有rowid最小的記錄

delete from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)

5、查找表中多餘的重複記錄（多個欄位），不包含rowid最小的記錄

select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)

6.消除一個欄位的左邊的第一位：

update tableName set [Title]=Right([Title],(len([Title])-1)) where Title like '村%'

7.消除一個欄位的右邊的第一位：

update tableName set [Title]=left([Title],(len([Title])-1)) where Title like '%村'

8.假刪除表中多餘的重複記錄（多個欄位），不包含rowid最小的記錄

update vitae set ispass=-1 where peopleId in (select peopleId from vitae group by peopleId,seq having count(*) > 1) and seq in （select seq from vitae group by peopleId,seq having count(*) > 1） and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)

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