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mysql查詢表里的重復(fù)數(shù)據(jù)方法

INSERT INTO hk_test(username, passwd) VALUES
('qmf1', 'qmf1'),('qmf2', 'qmf11')
 
delete from hk_test where username='qmf1' and passwd='qmf1'

MySQL里查詢表里的重復(fù)數(shù)據(jù)記錄：

先查看重復(fù)的原始數(shù)據(jù)：

場(chǎng)景一：列出username字段有重讀的數(shù)據(jù)

select username,count(*) as count from hk_test group by username having count>1;
 
SELECT username,count(username) as count FROM hk_test GROUP BY username HAVING count(username) >1 ORDER BY count DESC;

這種方法只是統(tǒng)計(jì)了該字段重復(fù)對(duì)應(yīng)的具體的個(gè)數(shù)

場(chǎng)景二：列出username字段重復(fù)記錄的具體指：

select * from hk_test where username in (select username from hk_test group by username having count(username) > 1)
 
SELECT username,passwd FROM hk_test WHERE username in ( SELECT username FROM hk_test GROUP BY username HAVING count(username)>1)
 
但是這條語(yǔ)句在mysql中效率太差，感覺mysql并沒有為子查詢生成臨時(shí)表。在數(shù)據(jù)量大的時(shí)候，耗時(shí)很長(zhǎng)時(shí)間

解決方法：

于是使用先建立臨時(shí)表 
 
create table `tmptable` as ( 
SELECT `name` 
FROM `table` 
GROUP BY `name` HAVING count(`name`) >1 
); 
 
然后使用多表連接查詢
 
SELECT a.`id`, a.`name` 
FROM `table` a, `tmptable` t 
WHERE a.`name` = t.`name`; 
 
結(jié)果這次結(jié)果很快就出來(lái)了。
 
用 distinct去重復(fù)
 
SELECT distinct a.`id`, a.`name` 
FROM `table` a, `tmptable` t 
WHERE a.`name` = t.`name`;

場(chǎng)景三：查看兩個(gè)字段都重復(fù)的記錄：比如username和passwd兩個(gè)字段都有重復(fù)的記錄：

select * from hk_test a
where (a.username,a.passwd) in (select username,passwd from hk_test group by username,passwd having count(*) > 1)

場(chǎng)景四：查詢表中多個(gè)字段同時(shí)重復(fù)的記錄：

select username,passwd,count(*) from hk_test group by username,passwd having count(*) > 1

MySQL查詢表內(nèi)重復(fù)記錄
 
查詢及刪除重復(fù)記錄的方法
(一)
1、查找表中多余的重復(fù)記錄，重復(fù)記錄是根據(jù)單個(gè)字段（peopleId）來(lái)判斷
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(fù)記錄，重復(fù)記錄是根據(jù)單個(gè)字段（peopleId）來(lái)判斷，只留有一個(gè)記錄
delete from people
where peopleId in (select peopleId 
from people group by peopleId having count(peopleId)>1)
and min(id) not 
in (select id from people group by peopleId having count(peopleId)>1)
 
3、查找表中多余的重復(fù)記錄（多個(gè)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、刪除表中多余的重復(fù)記錄（多個(gè)字段），只留有rowid最小的記錄
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(fù)記錄（多個(gè)字段），不包含rowid最小的記錄
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)
比方說(shuō)
在A表中存在一個(gè)字段“name”，而且不同記錄之間的“name”值有可能會(huì)相同，現(xiàn)在就是需要查詢出在該表中的各記錄之間，“name”值存在重復(fù)的項(xiàng)；
Select Name,Count(*) From A Group By Name Having Count(*) > 1
如果還查性別也相同大則如下:
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

SELECT * from tab1 where CompanyName in( SELECT companyname from tab1 GROUP BY CompanyName HAVING COUNT(*)>1);
-- 129.433ms 
 
SELECT * from tab1 INNER join ( SELECT companyname from tab1 GROUP BY CompanyName HAVING COUNT(*)>1) as tab2 USING(CompanyName);
-- 0.482ms
 
方法二
 
　　有兩個(gè)意義上的重復(fù)記錄，一是完全重復(fù)的記錄，也即所有字段均重復(fù)的記錄，二是部分關(guān)鍵字段重復(fù)的記錄，比如Name字段重復(fù)，而其他字段不一定重復(fù)或都重復(fù)可以忽略。
 
　　1、對(duì)于第一種重復(fù)，比較容易解決，使用
 
select distinct * from tableName
 
　　就可以得到無(wú)重復(fù)記錄的結(jié)果集。
 
　　如果該表需要?jiǎng)h除重復(fù)的記錄（重復(fù)記錄保留1條），可以按以下方法刪除
 
select distinct * into #Tmp from tableName
 
drop table tableName
 
select * into tableName from #Tmp
 
drop table #Tmp
 
　　發(fā)生這種重復(fù)的原因是表設(shè)計(jì)不周產(chǎn)生的，增加唯一索引列即可解決。
 
2、這類重復(fù)問(wèn)題通常要求保留重復(fù)記錄中的第一條記錄，操作方法如下
 
　　假設(shè)有重復(fù)的字段為Name,Address，要求得到這兩個(gè)字段唯一的結(jié)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)
 
最后一個(gè)select即得到了Name，Address不重復(fù)的結(jié)果集（但多了一個(gè)autoID字段，實(shí)際寫時(shí)可以寫在select子句中省去此列）
 
(四)查詢重復(fù)
 
select * from tablename where id in (
 
select id from tablename group by id having count(id) > 1)

常用的語(yǔ)句
 
1、查找表中多余的重復(fù)記錄，重復(fù)記錄是根據(jù)單個(gè)字段（mail_id）來(lái)判斷
 
 代碼如下 復(fù)制代碼 
 SELECT * FROM table WHERE mail_id IN (SELECT mail_id FROM table GROUP BY mail_id HAVING COUNT(mail_id) > 1);
 
 
2、刪除表中多余的重復(fù)記錄，重復(fù)記錄是根據(jù)單個(gè)字段（mail_id）來(lái)判斷，只留有rowid最小的記錄
 
 代碼如下 復(fù)制代碼 
DELETE FROM table WHERE mail_id IN (SELECT mail_id FROM table GROUP BY mail_id HAVING COUNT(mail_id) > 1) AND rowid NOT IN (SELECT MIN(rowid) FROM table GROUP BY mail_id HAVING COUNT(mail_id )>1);
 
 
3、查找表中多余的重復(fù)記錄（多個(gè)字段）
 
 代碼如下 復(fù)制代碼 
SELECT * FROM table WHERE (mail_id,phone) IN (SELECT mail_id,phone FROM table GROUP BY mail_id,phone HAVING COUNT(*) > 1);
 
 
4、刪除表中多余的重復(fù)記錄（多個(gè)字段），只留有rowid最小的記錄
 
 代碼如下 復(fù)制代碼 
 DELETE FROM table WHERE (mail_id,phone) IN (SELECT mail_id,phone FROM table GROUP BY mail_id,phone HAVING COU(www.jb51.net)NT(*) > 1) AND rowid NOT IN (SELECT MIN(rowid) FROM table GROUP BY mail_id,phone HAVING COUNT(*)>1);
 
 
5、查找表中多余的重復(fù)記錄（多個(gè)字段），不包含rowid最小的記錄
 
 代碼如下 復(fù)制代碼 
SELECT * FROM table WHERE (a.mail_id,a.phone) IN (SELECT mail_id,phone FROM table GROUP BY mail_id,phone HAVING COUNT(*) > 1) AND rowid NOT IN (SELECT MIN(rowid) FROM table GROUP BY mail_id,phone HAVING COUNT(*)>1);
 
 
存儲(chǔ)過(guò)程
 
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
 
 
 
(一)單個(gè)字段
 
1、查找表中多余的重復(fù)記錄，根據(jù)（question_title）字段來(lái)判斷
 
 代碼如下 復(fù)制代碼 
select * from questions where question_title in (select question_title from people group by question_title having count(question_title) > 1)
 
 
2、刪除表中多余的重復(fù)記錄，根據(jù)（question_title）字段來(lái)判斷，只留有一個(gè)記錄
 
 代碼如下 復(fù)制代碼 
delete from questions
where peopleId in (select peopleId from people group by peopleId having count(question_title) > 1)
and min(id) not in (select question_id from questions group by question_title having count(question_title)>1) 
 
(二)多個(gè)字段
 
刪除表中多余的重復(fù)記錄（多個(gè)字段），只留有rowid最小的記錄
 
 代碼如下 復(fù)制代碼 
DELETE FROM questions WHERE (questions_title,questions_scope) IN (SELECT questions_title,questions_scope FROM que(www.jb51.net)stions GROUP BY questions_title,questions_scope HAVING COUNT(*) > 1) AND question_id NOT IN (SELECT MIN(question_id) FROM questions GROUP BY questions_scope,questions_title HAVING COUNT(*)>1)
 
 
用上述語(yǔ)句無(wú)法刪除，創(chuàng)建了臨時(shí)表才刪的，求各位達(dá)人解釋一下。
 
 代碼如下 復(fù)制代碼 
CREATE TABLE tmp AS SELECT question_id FROM questions WHERE (questions_title,questions_scope) IN (SELECT questions_title,questions_scope FROM questions GROUP BY questions_title,questions_scope HAVING COUNT(*) > 1) AND question_id NOT IN (SELECT MIN(question_id) FROM questions GROUP BY questions_scope,questions_title HAVING COUNT(*)>1);
 
DELETE FROM questions WHERE question_id IN (SELECT question_id FROM tmp);
 
DROP TABLE tmp;

查找mysql數(shù)據(jù)表中重復(fù)記錄
mysql數(shù)據(jù)庫(kù)中的數(shù)據(jù)越來(lái)越多,當(dāng)然排除不了重復(fù)的數(shù)據(jù),在維護(hù)數(shù)據(jù)的時(shí)候突然想到要把多余的數(shù)據(jù)給刪減掉,剩下有價(jià)值的數(shù)據(jù)。

以下sql語(yǔ)句可以實(shí)現(xiàn)查找出一個(gè)表中的所有重復(fù)的記錄.
select user_name,count(*) as count from user_table group by user_name having count>1;

參數(shù)說(shuō)明:

user_name為要查找的重復(fù)字段.

count用來(lái)判斷大于一的才是重復(fù)的.

user_table為要查找的表名.

group by用來(lái)分組

having用來(lái)過(guò)濾.

把參數(shù)換成自己數(shù)據(jù)表的相應(yīng)字段參數(shù)，可以先在Phpmyadmin里面或者Navicat里面去運(yùn)行，看看有哪些數(shù)據(jù)重復(fù)了，然后在數(shù)據(jù)庫(kù)里面刪除掉，也可以直接將SQL語(yǔ)句放到后臺(tái)讀取新聞的頁(yè)面里面讀取出來(lái)，完善成查詢重復(fù)數(shù)據(jù)的列表，有重復(fù)的可以直接刪除。

效果如下：

缺點(diǎn)：這種方法的缺點(diǎn)就是當(dāng)你的數(shù)據(jù)庫(kù)里面的數(shù)據(jù)量很大的時(shí)候，效率很低，我用的是Navicat測(cè)試的，數(shù)據(jù)量不大，效率很高，當(dāng)然，網(wǎng)站還有其它查詢數(shù)據(jù)重復(fù)的SQL語(yǔ)句，舉一反三，大家好好研究研究，找到一個(gè)適合自己網(wǎng)站的查詢語(yǔ)句。

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