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查询数据库重复记录sql

时间:2022-06-29 07:51:17 编辑:袖梨 来源:一聚教程网


每条记录都有个hash字段,hash是把这条记录几个不同的字段组成唯一的值进行hash算法存的一个值,有了这个hash,可以判断记录是否重复,sql语句如下:


SELECT COUNT(*) as total ,`hash` FROM `js_receipt_detail` GROUP BY `hash` HAVING total > 1;

对hash进行group并筛选count个数大于1的。


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(*) >; 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

 

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
)

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