| 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 awhere (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 |
| 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 peoplewhere 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 peoplewhere 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 awhere (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 awhere (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 awhere (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 integerdeclare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >； 1open cur_rowsfetch cur_rows into @id,@maxwhile @@fetch_status=0beginselect @max = @max -1set rowcount @maxdelete from 表名 where 主字段 = @idfetch cur_rows into @id,@maxendclose cur_rowsset rowcount 0 |
