SQL查询及删除重复记录的方法

时间:2023-01-25 18:05:58

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

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

  1. delete from people   
  2. where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)  
  3. and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1)  
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)

  1. select * from vitae a  
  2. where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)  
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

  1. delete from vitae a  
  2. where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)  
  3. and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)  
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

  1. select * from vitae a  
  2. where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)  
  3. and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)  
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;

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


如果还查性别也相同大则如下:

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

(三) 方法一

  1. declare @max integer,@id integer  
  2.   
  3. declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >; 1  
  4.   
  5. open cur_rows  
  6.   
  7. fetch cur_rows into @id,@max  
  8.   
  9. while @@fetch_status=0  
  10.   
  11. begin  
  12.   
  13. select @max = @max -1  
  14.   
  15. set rowcount @max  
  16.   
  17. delete from 表名 where 主字段 = @id  
  18.   
  19. fetch cur_rows into @id,@max  
  20.   
  21. end  
  22.   
  23. close cur_rows  
  24.   
  25. set rowcount 0  
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

  1. select distinct * from tableName  
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

  1. select distinct * into #Tmp from tableName  
  2.   
  3. drop table tableName  
  4.   
  5. select * into tableName from #Tmp  
  6.   
  7. drop table #Tmp  
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

  1. select identity(int,1,1) as autoID, * into #Tmp from tableName  
  2.   
  3. select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID  
  4.   
  5. select * from #Tmp where autoID in(select autoID from #tmp2)  
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

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