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