SQL查询重复记录的多种方法介绍

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,seqhaving count(*) > 1)
and rowid not in (select min(rowid) from vitae group by peopleid,seq havingcount(*)>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,seqhaving count(*) > 1)
and rowid not in (select min(rowid) from vitae group by peopleid,seq havingcount(*)>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

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，使用以下语句就可以得到无重复记录的结果集。

select distinct * from tablename

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

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
)