数据库中查询及删除重复记录的方法大全_如何查询数据库里有没有重复的数据,有的话,删掉其余的。只留一个

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)

delete from gzseed_im_pic_zan a where (a.imid,a.picurl ) in (select  imid,picurl  from gzseed_im_pic_zan  group by  imid,picurl  having count(*) > 1)
and id not in (select min(id) from gzseed_im_pic_zan  group by imid,picurl having count(*)>1)

执行上面的报语法错误

delete from gzseed_im_pic_zan where (imid,picurl ) in (select  imid,picurl  from gzseed_im_pic_zan  group by  imid,picurl  having count(*) > 1)
and id not in (select min(id) from gzseed_im_pic_zan  group by imid,picurl having count(*)>1);

执行上面的报错：

You can't specify target table 'gzseed_im_pic_zan' for update in FROM clause

原因：

修改或者删除数据表的数据，判断条件不能再从同一个表中select ；创建临时表解决

复制一张表

复制数据到新表

 

drop table if EXISTS gzseed_im_pic_zan_temp;
/*复制表结构*/
 create table gzseed_im_pic_zan_temp select * from gzseed_im_pic_zan where 1=2;
/*复制表数据*/
insert into gzseed_im_pic_zan_temp select * from gzseed_im_pic_zan;


/*如果有重复记录，就删除重复的记录，保留记录中最早的记录*/ 
 delete  from gzseed_im_pic_zan  where ( imid, picurl) in (select b.imid,b.picurl from gzseed_im_pic_zan_temp b group by b.imid,b.picurl having count(*)>1)
  and id not in (select min(id) from gzseed_im_pic_zan_temp group by  imid,picurl 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(*) >； 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

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 tablename

group by id

having count(id) > 1

)