delete from 表名 where id not in (select d.id from (SELECT id FROM 表名 GROUP BY c1,c2,c3,c4)as d)
#去重复，把url重复，且区为空的中去掉。
select * from TABLE where url in (select u.url from (select * from TABLE where id not in (select d.id from (SELECT id FROM TABLE GROUP BY url)as d)) as u)and qu like "";
二、删除/去除重复记录
select *, count(distinct name) from table group by name
SELECT shortname,COUNT(*) FROM student GROUP BY shortname HAVING COUNT(*) > 1;
select user_name,count(*) as count from user group by user_name having count>1;
创建临时表：
create table tb2 select c1,c2 from tb1 group by c1,c2;
drop table tb1;
alter table tb2 rename to tb1;
三、统计重复数据：select c1,c2from tb1group by c1,c2having count(*)>1;除了GROUP BY 来读取数据表中不重复的数据，使用DISTINCT关键字来过滤。
用distinct:
select distinct c1,c2 from table;
四、防止表中出现重复数据：
在MySQL数据表中设置指定的字段为PRIMARY KEY索引/UNIQUE索引）来保证数据的唯一性。
create table tb1 (c1 char(16) not null,c2 char(16) not null,c3 char(10),primary key(c1,c2))或者：
create table tb1
(c1 char(20) not null,c2 char(20) not null,c3 char(10),unique(c1,c2))
mysql查询表里的重复数据方法
更新时间：2017年05月20日 13:51:47 投稿：mdxy-dxy
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
| 1 2 3 4 | 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
| 1 2 3 | 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：
| 1 2 3 4 5 | 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：
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | 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：
| 1 2 | 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：
| 1 | select username,passwd, count (*) from hk_test group by username,passwd having count (*) > 1 |
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 | 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 |
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 | 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。
MySQL之——查询重复记录、删除重复记录方法大全
查找所有重复标题的记录：
SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
一、查找重复记录
1、查找全部重复记录
Select * From 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1)
2、过滤重复记录(只显示一条)
Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)注：此处显示ID最大一条记录
二、删除重复记录
1、删除全部重复记录（慎用）
Delete 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1)
2、保留一条（这个应该是大多数人所需要的 ^_^）
Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title)注：此处保留ID最大一条记录
三、举例
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rowid最小的记录
delete from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1) and rowid not in (select min(rowid) 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)
四、补充
有两个以上的重复记录，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
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)
mysql 结果集去重复值并合并成一行
+——+——+
| id| name | tag |+——+——+|1 | 10| A|1 | 20| A|1 | 20| C|2 | 20| C|3 | 200 | B|3 | 500 | A+——+——+
以id分组，把name字段的值打印在一行，逗号分隔(默认)
select id,group_concat(name) from student group by id;以id分组，把name字段的值打印在一行，分号分隔：
select id,group_concat(name separator ’;’) from aa group by id;以id分组，把去冗余的name字段的值打印在一行，逗号分隔：
select id,group_concat(distinct name) from aa group by id;