mysql實現查重只留一個的方法：首先通過“select * from”查找表中多余的重復記錄；然后通過“delete from”刪除重復數據，并只保留一個數據即可。
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mysql 刪除重復數據只保留一條記錄
刪除重復數據保留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);
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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 子句設置條件的方式與 WHERE 和 SELECT 的交互方式類似。WHERE 搜索條件在進行分組操作之前應用；而 HAVING 搜索條件在進行分組操作之后應用。HAVING 語法與 WHERE 語法類似，但 HAVING 可以包含聚合函數。HAVING 子句可以引用選擇列表中顯示的任意項。)
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擴展：
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SQL：刪除重復數據，只保留一條用SQL語句,刪除掉重復項只保留一條在幾千條記錄里,存在著些相同的記錄,如何能用SQL語句,刪除掉重復的呢
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?1、查找表中多余的重復記錄，重復記錄是根據單個字段（peopleId）來判斷
select?*?from?people?where?peopleId?in?(select?peopleId?from?people?group?by?peopleId?having?count(peopleId)?>?1)
2、刪除表中多余的重復記錄，重復記錄是根據單個字段（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、查找表中多余的重復記錄（多個字段）
select?*?from?vitae?a?where?(a.peopleId,a.seq)?in?(select?peopleId,seq?from?vitae?group?by?peopleId,seq?having?count(*)?>?1)
4、刪除表中多余的重復記錄（多個字段），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、查找表中多余的重復記錄（多個字段），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.消除一個字段的左邊的第一位：
update?tableName?set?[Title]=Right([Title],(len([Title])-1))?where?Title?like?'村%'
7.消除一個字段的右邊的第一位：
update?tableName?set?[Title]=left([Title],(len([Title])-1))?where?Title?like?'%村'
8.假刪除表中多余的重復記錄（多個字段），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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