这篇文章主要介绍了mysql查询表里的重复数据方法,需要的朋友可以参考下
INSERT INTO hk_test(username, passwd) VALUES
('qmf1', 'qmf1'),('qmf2', 'qmf11')
delete from hk_test where username='qmf1' and passwd='qmf1'
MySQL里查询表里的重复数据记录：
先查看重复的原始数据：
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;
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
解决方法：
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`, 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)
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
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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
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.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 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 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.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) 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：
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。
