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mysql查询表里数据,mysql查询表里的重复数据方法

INSERT INTO hk_test(username, passwd) VALUES
('qmf1', 'qmf1'),('qmf2', 'qmf11')

delete from hk_test where username='qmf1' and passwd='qmf1'

mysql查询表里的双重数据情势,mysql查询表里数据

INSERT INTO hk_test(username, passwd) VALUES
('qmf1', 'qmf1'),('qmf2', 'qmf11')

delete from hk_test where username='qmf1' and passwd='qmf1'

图片 1

MySQL里询问表里的重复数据记录:

先查重视复的本来数据:

图片 2

情状一:列出username字段有重读的数额

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;

图片 3

这种办法只是计算了该字段重复对应的实际的个数

气象二:列出username字段重复记录的求实指:

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

图片 4

杀鸡取卵办法:

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`;

此情此景叁:查看三个字段都再也的笔录:比方username和passwd八个字段都有再一次的记录:

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

图片 5

情景四:查询表中多少个字段同时再一次的笔录:

select username,passwd,count(*) from hk_test group by username,passwd having count(*) > 1

图片 6

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

图片 7

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;

搜索mysql数据表中重复记录
mysql数据库中的数据进一步多,当然排除不了重复的数额,在体贴数据的时候突然想到要把剩余的多寡给删除掉,剩下有价值的数据。

以下sql语句能够兑现查寻觅二个表中的装有重复的记录.
select user_name,count(*) as count from user_table group by
user_name having count>1;

参数表明:

user_name为要物色的再度字段.

count用来判断大于1的才是双重的.

user_table为要探索的表名.

group by用来分组

having用来过滤.

把参数换到团结数据表的应和字段参数,能够先在Phpmyadmin里面可能Navicat里面去运转,看看有如何数据重复了,然后在数据Curry面删除掉,也能够直接将SQL语句放到后台读撤除息的页面里面读收取来,完善成查询重复数据的列表,有再度的能够一贯删除。

效益如下:

图片 8

症结:这种艺术的缺陷正是当您的数据Curry面包车型客车数据量一点都不小的时候,功效比十分低,笔者用的是Navicat测试的,数据量非常小,功能极高,当然,网站还有别的查询数据重复的SQL语句,举1反3,大家美好钻研研讨,找到叁个相符本人网址的查询语句。

INSERT INTO hk_test(username, passwd) VALUES(‘qmf1’, ‘qmf1’),(‘qmf2’,
‘qmf11’) delete from hk_test where username=’…

图片 9

MySQL里询问表里的重新数据记录:

先查正视复的固有数据:

图片 10

此情此景一:列出username字段有重读的数量

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;

图片 11

这种方法只是计算了该字段重复对应的切实的个数

场景二:列出username字段重复记录的有血有肉指:

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

图片 12

缓和方法:

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`;

情景三:查看八个字段都再也的笔录:比方username和passwd七个字段都有再次的记录:

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

图片 13

现象四:查询表中七个字段同时重复的笔录:

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