mysql查询表里的重复数据方法：

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mb5fe94d257d327 2015-10-12 15:08:00

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

mysql查询表里的重复数据方法：_删除表

MySQL里查询表里的重复数据记录：

先查看重复的原始数据：

mysql查询表里的重复数据方法：_表名_02

场景一：列出username字段有重读的数据

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查询表里的重复数据方法：_mysql_03

这种方法只是统计了该字段重复对应的具体的个数

场景二：列出username字段重复记录的具体指：

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查询表里的重复数据方法：_mysql_04

解决方法：

mysql查询表里的重复数据方法：_mysql_05

于是使用先建立临时表  复制代码 代码如下:  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 复制代码 代码如下:  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 复制代码 代码如下:  SELECT distinct a.`id`, a.`name`  FROM `table` a, `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：

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

mysql查询表里的重复数据方法：_mysql_06

场景四：查询表中多个字段同时重复的记录：

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

mysql查询表里的重复数据方法：_表名_07

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 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，只留有一个记录 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

mysql查询表里的重复数据方法：_mysql_08

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，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)

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) IN (SELECT mail_id,phone FROM table GROUP BY mail_id,phone HAVING COU(www.111cn.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 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);    存储过程   代码如下 复制代码  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 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.111cn.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) 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。

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;

参数说明:

user_name为要查找的重复字段.

count用来判断大于一的才是重复的.

user_table为要查找的表名.

group by用来分组

having用来过滤.

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。

效果如下：