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mysql查询表里的重复数据方法

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mbmwhfyn615732 显示全部楼层 发表于 2021-10-25 19:33:53 |阅读模式 打印 上一主题 下一主题
  1. INSERT INTO hk_test(username, passwd) VALUES
  2. ('qmf1', 'qmf1'),('qmf2', 'qmf11')
  3. 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:
先检察重复的原始数据:

场景一:列出username字段有重读的数据
  1. select username,count(*) as count from hk_test group by username having count>1;
  2. 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:
  1. select * from hk_test where username in (select username from hk_test group by username having count(username) > 1)
  2. SELECT username,passwd FROM hk_test WHERE username in ( SELECT username FROM hk_test GROUP BY username HAVING count(username)>1)
  3. 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
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办理方法:
  1. 于是使用先建立临时表
  2. create table `tmptable` as (
  3. SELECT `name`
  4. FROM `table`
  5. GROUP BY `name` HAVING count(`name`) >1
  6. );
  7. 然后使用多表连接查询
  8. SELECT a.`id`, a.`name`
  9. FROM `table` a, `tmptable` t
  10. WHERE a.`name` = t.`name`;
  11. 结果这次结果很快就出来了。
  12. 用 distinct去重复
  13. SELECT distinct a.`id`, a.`name`
  14. FROM `table` a, `tmptable` t
  15. WHERE a.`name` = t.`name`;
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场景三:检察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. select * from hk_test a
  2. 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:
  1. select username,passwd,count(*) from hk_test group by username,passwd having count(*) > 1
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  1. MySQL查询表内重复记录
  2. 查询及删除重复记录的方法
  3. (一)
  4. 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
  5. select *
  6. from people
  7. where peopleId in (select peopleId from people group by peopleId having count(peopleId)>1)
  8. 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
  9. delete from people
  10. where peopleId in (select peopleId
  11. from people group by peopleId having count(peopleId)>1)
  12. and min(id) not
  13. in (select id from people group by peopleId having count(peopleId)>1)
  14. 3、查找表中多余的重复记录(多个字段)
  15. select * from vitae a
  16. where (a.peopleId,a.seq) in
  17. (select peopleId,seq from vitae group by peopleId,seq having count(*)>1)
  18. 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
  19. delete from vitae a
  20. where
  21. (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq
  22. having count(*) > 1)
  23. and rowid not in (select min(rowid) from vitae group
  24. by peopleId,seq having count(*)>1)
  25. 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
  26. select * from vitae a
  27. where
  28. (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq
  29. having count(*) > 1)
  30. and rowid not in (select min(rowid) from vitae group
  31. by peopleId,seq having count(*)>1)
  32. (二)
  33. 比方说
  34. 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;
  35. Select Name,Count(*) From A Group By Name Having Count(*) > 1
  36. 如果还查性别也相同大则如下:
  37. Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1
  38. (三)
  39. 方法一
  40. declare @max integer,@id integer
  41. declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段
  42. having count(*) >; 1
  43. open cur_rows
  44. fetch cur_rows into @id,@max
  45. while @@fetch_status=0
  46. begin
  47. select @max = @max -1
  48. set rowcount @max
  49. delete from 表名 where 主字段 = @id
  50. fetch cur_rows into @id,@max
  51. end
  52. close cur_rows
  53. set rowcount 0
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  1. SELECT * from tab1 where CompanyName in( SELECT companyname from tab1 GROUP BY CompanyName HAVING COUNT(*)>1);
  2. -- 129.433ms
  3. SELECT * from tab1 INNER join ( SELECT companyname from tab1 GROUP BY CompanyName HAVING COUNT(*)>1) as tab2 USING(CompanyName);
  4. -- 0.482ms
  5. 方法二
  6.   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。
  7.   1、对于第一种重复,比较容易解决,使用
  8. select distinct * from tableName
  9.   就可以得到无重复记录的结果集。
  10.   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
  11. select distinct * into #Tmp from tableName
  12. drop table tableName
  13. select * into tableName from #Tmp
  14. drop table #Tmp
  15.   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。
  16. 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
  17.   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
  18. select identity(int,1,1) as autoID, * into #Tmp from tableName
  19. select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID
  20. select * from #Tmp where autoID in(select autoID from #tmp2)
  21. 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)
  22. (四)查询重复
  23. select * from tablename where id in (
  24. select id from tablename group by id having count(id) > 1)
  25. 常用的语句
  26. 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
  27. 代码如下 复制代码
  28. SELECT * FROM table WHERE mail_id IN (SELECT mail_id FROM table GROUP BY mail_id HAVING COUNT(mail_id) > 1);
  29. 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
  30. 代码如下 复制代码
  31. 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);
  32. 3、查找表中多余的重复记录(多个字段)
  33. 代码如下 复制代码
  34. SELECT * FROM table WHERE (mail_id,phone) IN (SELECT mail_id,phone FROM table GROUP BY mail_id,phone HAVING COUNT(*) > 1);
  35. 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
  36. 代码如下 复制代码
  37. 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);
  38. 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
  39. 代码如下 复制代码
  40. 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);
  41. 存储过程
  42. declare @max integer,@id integer
  43. declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >; 1
  44. open cur_rows
  45. fetch cur_rows into @id,@max
  46. while @@fetch_status=0
  47. begin
  48. select @max = @max -1
  49. set rowcount @max
  50. delete from 表名 where 主字段 = @id
  51. fetch cur_rows into @id,@max
  52. end
  53. close cur_rows
  54. set rowcount 0
  55. (一)单个字段
  56. 1、查找表中多余的重复记录,根据(question_title)字段来判断
  57. 代码如下 复制代码
  58. select * from questions where question_title in (select question_title from people group by question_title having count(question_title) > 1)
  59. 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
  60. 代码如下 复制代码
  61. delete from questions
  62. where peopleId in (select peopleId from people group by peopleId having count(question_title) > 1)
  63. and min(id) not in (select question_id from questions group by question_title having count(question_title)>1)
  64. (二)多个字段
  65. 删除表中多余的重复记录(多个字段),只留有rowid最小的记录
  66. 代码如下 复制代码
  67. 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)
  68. 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。
  69. 代码如下 复制代码
  70. 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);
  71. DELETE FROM questions WHERE question_id IN (SELECT question_id FROM tmp);
  72. DROP TABLE tmp;
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查找mysql数据表中重复记录
mysql数据库中的数据越来越多,固然清除不了重复的数据,在维护数据的时间忽然想到要把多余的数据给删减掉,剩下有代价的数据。
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用来判定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.
把参数换成本身数据表的相应字段参数,可以先在Phpmyadmin内里或者Navicat内里去运行,看看有哪些数据重复了,然后在数据库内里删撤除,也可以直接将SQL语句放到背景读取消息的页面内里读取出来,完满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内里的数据量很大的时间,效率很低,我用的是Navicat测试的,数据量不大,效率很高,固然,网站还有其它查询数据重复的SQL语句,闻一知十,各人好好研究研究,找到一个得当本身网站的查询语句。

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