查询和删除表中重复数据
查询和删除表中重复数据
文章分类:数据库?
若想将姓名、身份证号、住址这三个字段完全相同的记录查询出来?
select ? p1.* ? from ? persons ? p1,persons ? p2 ? where ? p1.id<>p2.id ? and ? p1.cardid ? = ? p2.cardid ? and ? p1.pname ? = ? p2.pname ? and ? p1.address ? = ? p2.address?
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可以实现上述效果．?
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几个删除重复记录的SQL语句?
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1.用rowid方法?
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2.用group by方法?
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3.用distinct方法?
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1。用rowid方法?
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据据oracle带的rowid属性，进行判断，是否存在重复,语句如下：?
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查数据:?
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?? ? select * from table1 a where rowid !=(select ? max(rowid)?
?? ? from table1 b where a.name1=b.name1 and a.name2=b.name2......)?
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删数据：?
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?? ?delete ? from table1 a where rowid !=(select ? max(rowid)?
?? ? from table1 b where a.name1=b.name1 and a.name2=b.name2......)?
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2.group by方法?
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查数据:?
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select count(num), max(name) from student --列出重复的记录数，并列出他的name属性?
group by num?
having count(num) >1 --按num分组后找出表中num列重复，即出现次数大于一次?
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删数据：?
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delete from student?
group by num?
having count(num) >1?
这样的话就把所有重复的都删除了。?
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3.用distinct方法 -对于小的表比较有用?
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create table table_new as ? select distinct * ? from table1 minux?
truncate table table1;?
insert into table1 select * from table_new;?
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查询及删除重复记录的方法大全?
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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)?
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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 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)?
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sql server不支持rowid?
我们可以变通实现同样的效果?
eg:?
delete from t_serviceitem?
where servid in (select servid from t_serviceitem group by servid having count(servid)>1)?
and gid not in (select min(gid) from t_serviceitem group by servid having count(servid )>1)?
(gid是该表PK)?
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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)?
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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)?
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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)?
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(二)?
比方说?
在A表中存在一个字段“name”，?
而且不同记录之间的“name”值有可能会相同，?
现在就是需要查询出在该表中的各记录之间，“name”值存在重复的项；?
Select Name,Count(*) From A Group By Name Having Count(*) > 1?
如果还查性别也相同大则如下:?
Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1?
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(三)?
方法一?
declare @max integer,@id integer?
declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >； 1?
open cur_rows?
fetch cur_rows into @id,@max?
while @@fetch_status=0?
begin?
select @max = @max -1?
set rowcount @max?
delete from 表名 where 主字段 = @id?
fetch cur_rows into @id,@max?
end?
close cur_rows?
set rowcount 0?
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方法二?
＂重复记录＂有两个意义上的重复记录，一是完全重复的记录，也即所有字段均重复的记录，二是部分关键字段重复的记录，比如Name字段重复，而其他字段不一定重复或都重复可以忽略。?
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1、对于第一种重复，比较容易解决，使用?
select distinct * from tableName?
就可以得到无重复记录的结果集。?
如果该表需要删除重复的记录（重复记录保留1条），可以按以下方法删除?
select distinct * into #Tmp from tableName?
drop table tableName?
select * into tableName from #Tmp?
drop table #Tmp?
发生这种重复的原因是表设计不周产生的，增加唯一索引列即可解决。?
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2、这类重复问题通常要求保留重复记录中的第一条记录，操作方法如下?
假设有重复的字段为Name,Address，要求得到这两个字段唯一的结果集?
select identity(int,1,1) as autoID, * into #Tmp from tableName?
select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID?
select * from #Tmp where autoID in(select autoID from #tmp2)?
最后一个select即得到了Name，Address不重复的结果集（但多了一个autoID字段，实际写时可以写在select子句中省去此列）?
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(四)?
查询重复?
select * from tablename where id in (?
select id from tablename?
group by id?
having count(id) > 1?