1、在面试的时候碰到一个 问题，就是让写一张表中有id和name 两个字段，查询出name重复的所有数据，现在列下：SELECT * from xi a where (a.username) in (SELECT username from xi group by username having count(*) > 1)

2、查询出所有数据进行分组之后，和重复数据的重复次数的查询数据，先列下：SELECT count(username) as '重复次数',username from xi group by username having count(*)>1 order by username desc

3、一下为 查看别人的 结果，现列下：查询及删除重复记录的方法大全

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 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)

另外，MySQL中使用上面的SQL会报错：You can't specify target table 'XXX' for update in FROM clause,不能在修改表的同时去查询同一张表，因此可以像下面的语句一样，将查询结果命名为一张临时表来作为修改表数据的条件，以规避上述错误。DELETE from user where user_id in(

(SELECT user_id from

(SELECT c.* from cab_user c where c.extra_id in

(SELECT a.extra_id from user a group by a.extra_id having count(a.extra_id) > 1) and c.user_id not in

(SELECT min(b.user_id) from user b group by b.extra_id having count(b.extra_id )>1)

) d

)

)

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)

(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

(三)

方法一declare @max integer,@id integerdeclare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >； 1open cur_rowsfetch cur_rows into @id,@maxwhile @@fetch_status=0beginselect @max = @max -1set rowcount @maxdelete from 表名 where 主字段 = @idfetch cur_rows into @id,@maxendclose cur_rowsset rowcount 0

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。

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 tableNamedrop table tableNameselect * into tableName from #Tmpdrop 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。

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 tableNameselect min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoIDselect * 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)

(四)查询重复SELECT * from tablename where id in (select id from tablenamegroup by idhaving count(id) > 1)

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