SQL重复记录查询 查询多个字段、多表查询、删除重复记录的方法

时间:2022-04-04 21:19:23

SQL重复记录查询

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 

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select * from people
where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)

例二: 

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select * from testtable
where numeber in (select number from people group by number having count(number) > 1 )

可以查出testtable表中number相同的记录  

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 

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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)  

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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 

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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 

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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; 

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Select Name,Count(*) From A Group By Name Having Count(*) > 1

如果还查性别也相同大则如下: 

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Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1

(三) 

方法一 

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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 

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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 

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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 

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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 

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select * from tablename where id in (
 
select id from tablename 
 
group by id 
 
having count(id) > 1
 
)

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