前言
本文主要給大家介紹了關於MySQL中查詢、刪除重復記錄的方法，分享出來供大家參考學習，下面來看看詳細的介紹：
查找所有重復標題的記錄：
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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、查找重復記錄
1、查找全部重復記錄
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1
|
SELECT
*
FROM
t_info a
WHERE
((
SELECT
COUNT
(*)
FROM
t_info
WHERE
Title = a.Title) > 1)
ORDER
BY
Title
DESC
|
2、過濾重復記錄(只顯示一條)
|
1
|
Select
*
From
HZT
Where
ID
In
(
Select
Max
(ID)
From
HZT
Group
By
Title)
|
注：此處顯示ID最大一條記錄
二、刪除重復記錄
1、刪除全部重復記錄（慎用）
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1
|
Delete
表
Where
重復字段
In
(
Select
重復字段
From
表
Group
By
重復字段
Having
Count
(*)>1)
|
2、保留一條（這個應該是大多數人所需要的 ^_^）
|
1
|
Delete
HZT
Where
ID
Not
In
(
Select
Max
(ID)
From
HZT
Group
By
Title)
|
注：此處保留ID最大一條記錄
三、舉例
1、查找表中多余的重復記錄，重復記錄是根據單個字段（peopleId）來判斷
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1
|
select
*
from
people
where
peopleId
in
(
select
peopleId
from
people
group
by
peopleId
having
count
(peopleId) > 1)
|
2、刪除表中多余的重復記錄，重復記錄是根據單個字段（peopleId）來判斷，只留有rowid最小的記錄
|
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、查找表中多余的重復記錄（多個字段）
|
1
|
select
*
from
vitae a
where
(a.peopleId,a.seq)
in
(
select
peopleId,seq
from
vitae
group
by
peopleId,seq
having
count
(*) > 1)
|
4、刪除表中多余的重復記錄（多個字段），只留有rowid最小的記錄
|
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、查找表中多余的重復記錄（多個字段），不包含rowid最小的記錄
|
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、補充
有兩個以上的重復記錄，一是完全重復的記錄，也即所有字段均重復的記錄，二是部分關鍵字段重復的記錄，比如Name字段重復，而其他字段不一定重復或都重復可以忽略。
1、對於第一種重復，比較容易解決，使用
|
1
|
select
distinct
*
from
tableName
|
就可以得到無重復記錄的結果集。
如果該表需要刪除重復的記錄（重復記錄保留1條），可以按以下方法刪除
|
1
2
3
4
|
select
distinct
*
into
#Tmp
from
tableName
drop
table
tableName
select
*
into
tableName
from
#Tmp
drop
table
#Tmp
|
發生這種重復的原因是表設計不周產生的，增加唯一索引列即可解決。
2、這類重復問題通常要求保留重復記錄中的第一條記錄，操作方法如下
假設有重復的字段為Name,Address，要求得到這兩個字段唯一的結果集
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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)
|
總結
以上就是這篇文章的全部內容了，希望本文的內容對大家的學習或者工作能帶來一定的幫助
原文鏈接：http://blog.phpsoho.com/2017/06/20/mysql之-查詢重復記錄、刪除重復記錄方法大全/