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用sql语句，删除掉重复项只保留一条

在几千条记录里，存在着些相同的记录，如何能用sql语句，删除掉重复的呢

1、查找表中多余的重复记录，重复记录是根据单个字段(peopleid)来判断

select * from people

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

2、删除表中多余的重复记录，重复记录是根据单个字段(peopleid)来判断，只留有rowid最小的记录

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、查找表中多余的重复记录(多个字段)

select * from vitae a

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

4、删除表中多余的重复记录(多个字段)，只留有rowid最小的记录

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、查找表中多余的重复记录(多个字段)，不包含rowid最小的记录

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.消除一个字段的左边的第一位：

update tablename set [title]=right([title],(len([title])-1)) where title like '村%'

7.消除一个字段的右边的第一位：

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

8.假删除表中多余的重复记录(多个字段)，不包含rowid最小的记录

update vitae set ispass=-1

where peopleid in (select peopleid from vitae group by peopleid

alter table mytable drop index mdl_tag_use_ix;//mdl_tag_use_ix是上表查出的索引名，key_name

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