前言
本文主要给大家介绍了关于MySQL中查询、删除重复记录的方法，分享出来供大家参考学习，下面来看看详细的介绍：
查找所有重复标题的记录：
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1
|
select
title,
count
(*)
as
count
from
user_table
group
by
title
having
count
>1;
|
|
1
|
SELECT
*
FROM
t_info a
WHERE
((
SELECT
COUNT
(*)
FROM
t_info
WHERE
Title = a.Title) > 1)
ORDER
BY
Title
DESC
|
一、查找重复记录
1、查找全部重复记录
|
1
|
SELECT
*
FROM
t_info a
WHERE
((
SELECT
COUNT
(*)
FROM
t_info
WHERE
Title = a.Title) > 1)
ORDER
BY
Title
DESC
|
2、过滤重复记录(只显示一条)
|
1
|
Select
*
From
HZT
Where
ID
In
(
Select
Max
(ID)
From
HZT
Group
By
Title)
|
注：此处显示ID最大一条记录
二、删除重复记录
1、删除全部重复记录（慎用）
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1
|
Delete
表
Where
重复字段
In
(
Select
重复字段
From
表
Group
By
重复字段
Having
Count
(*)>1)
|
2、保留一条（这个应该是大多数人所需要的 ^_^）
|
1
|
Delete
HZT
Where
ID
Not
In
(
Select
Max
(ID)
From
HZT
Group
By
Title)
|
注：此处保留ID最大一条记录
三、举例
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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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
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
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
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
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)
|
四、补充
有两个以上的重复记录，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
|
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
2
3
4
|
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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1
2
3
|
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)
|
总结
以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作能带来一定的帮助
原文链接：http://blog.phpsoho.com/2017/06/20/mysql之-查询重复记录、删除重复记录方法大全/