mysql資料庫如何去除重複資料

mysql資料庫去除重複資料的方法：1、查詢需要刪除的記錄，會保留一條記錄；2、刪除重複記錄，只保留一條記錄，程式碼為【delete a from test1 a, (...)as bid from test1 c where..】。

mysql資料庫去除重複資料的方法：

1、查詢需要刪除的記錄，會保留一條記錄。

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、刪除重複記錄，只保留一條記錄。注意，subject,RECEIVER 要索引，否則會很慢的。

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、查詢表中多餘的重複記錄，重複記錄是根據單個欄位（peopleId）來判斷

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

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

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)

看來想偷懶使用一句命令完成這個事好像不太顯示，還是老老實實的分步處理吧，思路先建立複製一個臨時表，然後對比臨時表內的資料，刪除主表裡的資料

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;

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