MySQL根据某一个或者多个字段查找重复数据的sql语句

sql 查出一张表中重复的所有记录数据

1.表中有id和name 两个字段，查询出name重复的所有数据

 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)

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 integer
declare cur_rows cursor local for 
select 主字段,count(*) from 表名 group by 主字段 having count(*) >;
open cur_rows fetch cur_rows into @id,@maxwhile @@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,@maxend
close cur_rows
set 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 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。

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）

(四)查询重复

 select * from tablename where id in (select id from tablenamegroup by idhaving count(id) > 1)

对一个字段查找重复记录

根据sample_code字段找到重复记录

select * from tb_table where sample_code in( select sample_code from tb_table group by sample_code having count(sample_code) > 1 );

对多个字段查找重复记录（这里以2个为例）

根据name和code字段找到重复记录

select * from (select *, concat(name,code) as nameandcode from tb_table) t where t.nameandcode in 
(
 select nameandcode from (select concat(name,code) as nameandcode from tb_table) tt group by nameandcode having count(nameandcode) > 1
)

总结

以上所述是小编给大家介绍的mysql根据某一个或者多个字段查找重复数据的sql语句，希望对大家有所帮助