sql去除重复语句

小灰灰 2022-06-18 07:12 225阅读 0赞

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) ;  
  
  
  
  
**查询表中前5条记录：**  
  
  
select \* from 表1 limit 5;    
   
select \* from 表1 limit 0,5;   
  
  
查询表中第5条到第7条记录：  
  
  
select \* from 表1 limit 4,3;   
  
  
**随即选取一个记录：**  
  
  
select \* from 表1 order by rand() limit 1;    
  
  
**随即选取n条记录：**  
  
  
select \* from 表1 order by rand() limit n;    
  
  
  
  
**MySQL查询结果按某值排序**  
  
  
select \* from test where id in(3,1,5);    
  
  
select \* from test where id in(3,1,5) order by find\_in\_set(id,'3,1,5');    
select \* from test where id in(3,1,5) order by substring\_index('3,1,2',id,1);    
  
  
  
**sql 单表/多表查询去除重复记录**

单表distinct

多表group by

group by 必须放在 order by 和 limit之前，不然会报错

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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

＂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

)

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)

运行会产生问题，where(a.peopleId,a.seq)这样的写发是通不过的！！！   
  
  
mysql 重复记录只选取最后一条  
  
  
  
  
\# sid相同，create\_time不同，取create\_time最后一条  
  
  
1. **使用 NOT EXISTS参数**  
SELECT id, sid FROM table\_name a WHERE NOT EXISTS (SELECT 1 FROM table\_name where a.sid = sid AND a.create\_time < create\_time)   
  
  
2. **使用子查询**  
SELECT id, sid FROM table\_name WHERE create\_time IN (SELECT max(create\_time) FROM table\_name group by sid)