INSERT INTO hk_test(username, passwd) VALUES('qmf1', 'qmf1'),('qmf2', 'qmf11') delete from hk_test where username='qmf1' and passwd='qmf1'

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;

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

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`;

select * from hk_test awhere (a.username,a.passwd) in (select username,passwd from hk_test group by username,passwd having count(*) > 1)

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

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 　　有兩個意義上的重復記錄，一是完全重復的記錄，也即所有字段均重復的記錄，二是部分關鍵字段重復的記錄，比如Name字段重復，而其他字段不一定重復或都重復可以忽略。 　　1、對于第一種重復，比較容易解決，使用 select distinct * from tableName 　　就可以得到無重復記錄的結果集。 　　如果該表需要刪除重復的記錄（重復記錄保留1條），可以按以下方法刪除 select distinct * into #Tmp from tableName drop table tableName select * into tableName from #Tmp drop table #Tmp 　　發生這種重復的原因是表設計不周產生的，增加唯一索引列即可解決。 2、這類重復問題通常要求保留重復記錄中的第一條記錄，操作方法如下 　　假設有重復的字段為Name,Address，要求得到這兩個字段唯一的結果集 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) 最后一個select即得到了Name，Address不重復的結果集（但多了一個autoID字段，實際寫時可以寫在select子句中省去此列） (四)查詢重復 select * from tablename where id in ( select id from tablename group by id having count(id) > 1)常用的語句 1、查找表中多余的重復記錄，重復記錄是根據單個字段（mail_id）來判斷  代碼如下 復制代碼  SELECT * FROM table WHERE mail_id IN (SELECT mail_id FROM table GROUP BY mail_id HAVING COUNT(mail_id) > 1);  2、刪除表中多余的重復記錄，重復記錄是根據單個字段（mail_id）來判斷，只留有rowid最小的記錄  代碼如下 復制代碼 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、查找表中多余的重復記錄（多個字段）  代碼如下 復制代碼 SELECT * FROM table WHERE (mail_id,phone) IN (SELECT mail_id,phone FROM table GROUP BY mail_id,phone 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  代碼如下 復制代碼  DELETE FROM table WHERE (mail_id,phone) IN (SELECT mail_id,phone FROM table GROUP BY mail_id,phone HAVING COU(www.49028c.com)NT(*) > 1) AND rowid NOT IN (SELECT MIN(rowid) FROM table GROUP BY mail_id,phone HAVING COUNT(*)>1);  5、查找表中多余的重復記錄（多個字段），不包含rowid最小的記錄  代碼如下 復制代碼 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);  存儲過程 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)單個字段 1、查找表中多余的重復記錄，根據（question_title）字段來判斷  代碼如下 復制代碼 select * from questions where question_title in (select question_title from people group by question_title having count(question_title) > 1)  2、刪除表中多余的重復記錄，根據（question_title）字段來判斷，只留有一個記錄  代碼如下 復制代碼 delete from questionswhere 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)多個字段 刪除表中多余的重復記錄（多個字段），只留有rowid最小的記錄  代碼如下 復制代碼 DELETE FROM questions WHERE (questions_title,questions_scope) IN (SELECT questions_title,questions_scope FROM que(www.49028c.com)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)  用上述語句無法刪除，創建了臨時表才刪的，求各位達人解釋一下。  代碼如下 復制代碼 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;