| INSERT INTO hk_test(username, passwd) VALUES('qmf1', 'qmf1'),('qmf2', 'qmf11') delete from hk_test where username='qmf1' and passwd='qmf1' |
MySQL里查詢表里的重復數據記錄：
先查看重復的原始數據：
場景一：列出username字段有重讀的數據
| 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; |
這種方法只是統計了該字段重復對應的具體的個數
場景二：列出username字段重復記錄的具體指：
| 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) 但是這條語句在mysql中效率太差，感覺mysql并沒有為子查詢生成臨時表。在數據量大的時候，耗時很長時間 |
解決方法：
| 于是使用先建立臨時表 create table `tmptable` as ( SELECT `name` FROM `table` GROUP BY `name` HAVING count(`name`) >1 ); 然后使用多表連接查詢 SELECT a.`id`, a.`name` FROM `table` a, `tmptable` t WHERE a.`name` = t.`name`; 結果這次結果很快就出來了。 用 distinct去重復 SELECT distinct a.`id`, a.`name` FROM `table` a, `tmptable` t WHERE a.`name` = t.`name`; |
場景三：查看兩個字段都重復的記錄：比如username和passwd兩個字段都有重復的記錄：
| select * from hk_test awhere (a.username,a.passwd) in (select username,passwd from hk_test group by username,passwd having count(*) > 1) |
場景四：查詢表中多個字段同時重復的記錄：
| select username,passwd,count(*) from hk_test group by username,passwd having count(*) > 1 |
| MySQL查詢表內重復記錄 查詢及刪除重復記錄的方法(一)1、查找表中多余的重復記錄，重復記錄是根據單個字段（peopleId）來判斷select * from peoplewhere peopleId in (select peopleId from people group by peopleId having count(peopleId)>1) 2、刪除表中多余的重復記錄，重復記錄是根據單個字段（peopleId）來判斷，只留有一個記錄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、查找表中多余的重復記錄（多個字段）select * from vitae awhere (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*)>1) 4、刪除表中多余的重復記錄（多個字段），只留有rowid最小的記錄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、查找表中多余的重復記錄（多個字段），不包含rowid最小的記錄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)比方說在A表中存在一個字段“name”，而且不同記錄之間的“name”值有可能會相同，現在就是需要查詢出在該表中的各記錄之間，“name”值存在重復的項；Select Name,Count(*) From A Group By Name Having Count(*) > 1如果還查性別也相同大則如下: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 |
