MySQL 刪除數據庫中反復數據辦法小結

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剛開端，依據我的設法主意，這個很簡略嘛，上sql語句

delete from zqzrdp where tel in (select min(dpxx_id) from zqzrdp group by tel having count(tel)>1);

履行，報錯！！~！~

異常意為：你不克不及指定目的表的更新在FROM子句。傻了，MySQL 如許寫，不可，讓人愁悶。

難倒只能分步操作，蛋疼

以下是網友寫的，異樣是坑爹的代碼，我機械上運轉不了。

1. 查詢須要刪除的記載，會保存一筆記錄。

select a.id,a.subject,a.RECEIVER from test1 a left join (select c.subject,c.RECEIVER ,max(c.id) as bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having count(1) >1) b on a.id< b.bid where a.subject=b.subject and a.RECEIVER = b.RECEIVER and a.id < b.bid

2. 刪除反復記載，只保存一筆記錄。留意，subject,RECEIVER 要索引，不然會很慢的。

delete a from test1 a, (select c.subject,c.RECEIVER ,max(c.id) as bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having count(1) >1) b where a.subject=b.subject and a.RECEIVER = b.RECEIVER and a.id < b.bid;

3. 查找表中過剩的反復記載，反復記載是依據單個字段（peopleId）來斷定

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

4. 刪除表中過剩的反復記載，反復記載是依據單個字段（peopleId）來斷定，只留有rowid最小的記載

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

5.刪除表中過剩的反復記載（多個字段），只留有rowid最小的記載

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)

看來想偷懶應用一句敕令完成這個事似乎不太顯示，照樣老誠實實的分步處置吧，思緒先樹立復制一個暫時表，然後比較暫時表內的數據，刪除主內外的數據

alter table tableName add autoID int auto_increment not null; 

create table tmp select min(autoID) as autoID from tableName group by Name,Address; 

create table tmp2 select tableName.* from tableName,tmp where tableName.autoID = tmp.autoID; 

drop table tableName; 

rename table tmp2 to tableName;