mysql查询表里的重复数据方法和删除重复数据
mysql查询表里的重复数据方法:
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INSERT INTO hk_test(username, passwd) VALUES ( 'qmf1' , 'qmf1' ),( 'qmf2' , 'qmf11' )
delete from hk_test where username= 'qmf1' and passwd= 'qmf1'
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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
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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;
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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:
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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:
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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`; |
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select * from hk_test a where (a.username,a.passwd) in (select username,passwd from hk_test group by username,passwd having count(*) > 1 )
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场景四:查询表中多个字段同时重复的记录:
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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
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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 )
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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:
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。