mysql 数据表中查找、删除重复记录

为了性能考虑，在阅读之前提醒大家，如果有子查询，子查询查询到的数据最好不要超过总数据量的30%。

查询有重复数据的记录

select * from F group by a,b,c,d having count(*)>1

select distinct * into #Tmp from tableName
drop table tableName
select * into tableName from #Tmp
drop table #Tmp

SQL删除重复数据方法

例如：

id           name         value
1               a                 pp
2               a                 pp
3               b                 iii
4               b                 pp
5               b                 pp
6               c                 pp
7               c                 pp
8               c                 iii

id是主键
要求得到这样的结果

id           name         value
1               a                 pp
3               b                 iii
4               b                 pp
6               c                 pp
8               c                 iii

方法1

delete YourTable where [id] not in ( select max([id]) from YourTable group by (name + value))

方法2

delete a from 表 a left join( select id=min(id) from 表 group by name,value )b on a.id=b.id where b.id is null

查询及删除重复记录的SQL语句 查询及删除重复记录的SQL语句

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 )

去重：

-- //////////////////////////////////实现1
DELETE t1.*
FROM
tableName t1
WHERE
t1.id NOT IN (
SELECT
*
FROM
(
SELECT
min(t3.id)
FROM
tableName t3
GROUP BY
column1
) t2
) -- //////////////////////////////////实现2
DELETE t1.*
FROM
tableName t1
WHERE
t1.id NOT IN (
SELECT
*
FROM
(
SELECT DISTINCT
id
FROM
tableName t3
) t2
)