MYSQL教程mysql查询表里的重复数据方法

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《MysqL教程mySQL查询表里的重复数据方法》要点：
本文介绍了MysqL教程mySQL查询表里的重复数据方法，希望对您有用。如果有疑问，可以联系我们。

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

MysqL入门

MysqL里查询表里的重复数据记录：MysqL入门

先查看重复的原始数据：MysqL入门

MysqL入门

场景一：列出username字段有重读的数据
MysqL入门

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;

MysqL入门

这种方法只是统计了该字段重复对应的具体的个数MysqL入门

场景二：列出username字段重复记录的具体指：MysqL入门

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) 但是这条语句在MysqL中效率太差,感觉MysqL并没有为子查询生成临时表.在数据量大的时候,耗时很长时间

MysqL入门

解决方法：MysqL入门

于是使用先建立临时表  create table `tmptable` as ( SELECT `name` FROM `table` GROUP BY `name` HAVING count(`name`) >1 );  然后使用多表连接查询 SELECT a.`ID`,a.`name` FROM `table` a,`tmptable` t WHERE a.`name` = t.`name`;  结果这次结果很快就出来了. 用 distinct去重复 SELECT distinct a.`ID`,`tmptable` t WHERE a.`name` = t.`name`;

场景三：查看两个字段都重复的记录：比如username和passwd两个字段都有重复的记录：MysqL入门

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

MysqL入门

场景四：查询表中多个字段同时重复的记录：MysqL入门

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

MysqL入门

MySQL查询表内重复记录 查询及删除重复记录的方法(一)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 peoplewhere 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,只留有一个记录delete from peoplewhere 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、查找表中多余的重复记录(多个字段)select * from vitae awhere (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 awhere (a.peopleID,a.seq) in (select 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 awhere (a.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 integerdeclare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >； 1open cur_rowsfetch cur_rows into @ID,@maxwhile @@fetch_status=0beginselect @max = @max -1set rowcount @maxdelete from 表名 where 主字段 = @IDfetch cur_rows into @ID,@maxendclose cur_rowsset rowcount 0

MysqL入门

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, *** 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)常用的语句 1、查找表中多余的重复记录,重复记录是根据单个字段(mail_ID)来判断  代码如下 复制代码  SELECT * FROM table WHERE mail_ID IN (SELECT mail_ID FROM table GROUP BY mail_ID HAVING COUNT(mail_ID) > 1);  2、删除表中多余的重复记录,重复记录是根据单个字段(mail_ID)来判断,只留有rowID最小的记录  代码如下 复制代码 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、查找表中多余的重复记录(多个字段)  代码如下 复制代码 SELECT * FROM table WHERE (mail_ID,phone) IN (SELECT mail_ID,phone FROM table GROUP BY mail_ID,phone 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  代码如下 复制代码  DELETE FROM table WHERE (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、查找表中多余的重复记录(多个字段),不包含rowID最小的记录  代码如下 复制代码 SELECT * FROM table WHERE (a.mail_ID,a.phone) IN (SELECT mail_ID,phone HAVING COUNT(*) > 1) AND rowID NOT IN (SELECT MIN(rowID) FROM table GROUP BY mail_ID,phone HAVING COUNT(*)>1);  存储过程 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)单个字段 1、查找表中多余的重复记录,根据(question_Title)字段来判断  代码如下 复制代码 select * from questions where question_Title in (select question_Title from people group by question_Title having count(question_Title) > 1)  2、删除表中多余的重复记录,根据(question_Title)字段来判断,只留有一个记录  代码如下 复制代码 delete from questionswhere 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)多个字段 删除表中多余的重复记录(多个字段),只留有rowID最小的记录  代码如下 复制代码 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)  用上述语句无法删除,创建了临时表才删的,求各位达人解释一下.  代码如下 复制代码 CREATE table tmp AS SELECT question_ID FROM questions WHERE (questions_Title,questions_scope FROM questions GROUP BY questions_Title,questions_Title HAVING COUNT(*)>1); DELETE FROM questions WHERE question_ID IN (SELECT question_ID FROM tmp); DROP table tmp;

查找MysqL数据表中重复记录
MysqL数据库中的数据越来越多,当然排除不了重复的数据,在维护数据的时候突然想到要把多余的数据给删减掉,剩下有价值的数据.MysqL入门

以下SQL语句可以实现查找出一个表中的所有重复的记录.
select user_name,count(*) as count from user_table group by user_name having count>1;MysqL入门

参数说明:MysqL入门

user_name为要查找的重复字段.MysqL入门

count用来判断大于一的才是重复的.MysqL入门

user_table为要查找的表名.MysqL入门

group by用来分组MysqL入门

having用来过滤.MysqL入门

把参数换成自己数据表的相应字段参数,可以先在phpmyadmin里面或者Navicat里面去运行,看看有哪些数据重复了,然后在数据库里面删除掉,也可以直接将SQL语句放到后台读取新闻的页面里面读取出来,完善成查询重复数据的列表,有重复的可以直接删除.MysqL入门

效果如下：MysqL入门

MysqL入门

缺点：这种方法的缺点就是当你的数据库里面的数据量很大的时候,效率很低,我用的是Navicat测试的,数据量不大,效率很高,当然,网站还有其它查询数据重复的SQL语句,举一反三,大家好好研究研究,找到一个适合自己网站的查询语句.MysqL入门

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