mysqlrowid的简单介绍
本篇文章给大家谈谈mysqlrowid,以及对应的知识点,希望对各位有所帮助,不要忘了收藏本站喔。
本文目录一览:
- 1、Mysql根据一张表俩个字段删除重复数据
- 2、MySQL查询出现重复列名,重复列只保留最后一列
- 3、请教关于mysql有没有rowid
- 4、mysql去重复 保留一条
- 5、SQL自动编号 rowid是怎么执行?是再创建一张表么?
Mysql根据一张表俩个字段删除重复数据
如果你需要的是删除数清拦据库中的数据:激碰
delete from table a
where (a.user_id,a.tw_id) in (select user_id,tw_id from vitae group by user_id,tw_id having count(*) 明正谈 1)
and rowid not in (select min(rowid) from vitae group by user_id,tw_id having count(*)1)
如果只是查出是去重:
select distinct user_id,tw_id from table
[img]MySQL查询出现重复列名,重复列只保留最后一列
MySQL查询重复字段,及删除重复记录的方法
MySQL, 数据库, 数据库, 字段, 服务器
数据库中有个大表,需要查找其中的名字有重复的记录id,以便比较。如果仅仅是查找数据库中name不野告重复的字段,很容易:
SELECT min(`id`),`name` FROM `table` GROUP BY `name`;
但是这样并不能得到说有重复字段的id值。(只得到了最小的一个id值)查询哪些字段是重复的颂贺明也容易:
SELECT `name`,count(`name`) as count FROM `table` GROUP BY `name` HAVING count(`name`) 1 ORDER BY count DESC;
但是要一次查询到重复字段的id值,就必须使用子查询了,于是使用下面的语句。
SELECT `id`,`name` FROM `table` WHERE `name` in (
SELECT `name`
FROM `table`
GROUP BY `name` HAVING count(`name`) 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零时表。于是使用先建立零时表:
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。
========================
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,重复拍燃记录是根据单个字段(peopleId)来判断,只留有rowid最小的记录
delete from people
where peopleId in (select peopleId from people group by peopleId having count(peopleId) 1)
and rowid not in (select min(rowid) 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
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,二是部分关键词段重复的记录,比如Name字段重复,而其它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
)
请教关于mysql有没有rowid
MYSQL没有念滚隐卜高正藏的rowid字段,这和informix、oracle等型悔不一样的,要操作数据必须自己使用表上的主键。
mysql去重复 保留一条
mysql去重复 保留一条怎么操作呢?一起来看下吧:
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 弯迹( 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rowid最小的记录
DELETE FROM people WHERE peopleName IN ( SELECT peopleName FROM people GROUP BY peopleName HAVING count(peopleName) 1 ) AND peopleId NOT IN ( SELECT min(peopleId) FROM people GROUP BY peopleName HAVING count(peopleName) 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, 衫轮 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 )
6、消除一个字段的左边的埋塌并第一位:
UPDATE tableName SET [ Title ]= RIGHT ([ Title ],(len([ Title ]) - 1)) WHERE Title LIKE '村%'
7、消除一个字段的右边的第一位:
UPDATE tableName SET [ Title ]= LEFT ([ Title ],(len([ Title ]) - 1)) WHERE Title LIKE '%村'
8、假删除表中多余的重复记录(多个字段),不包含rowid最小的记录
UPDATE vitae SET ispass =- 1 WHERE peopleId IN ( SELECT peopleId FROM vitae GROUP BY peopleId
SQL自动编号 rowid是怎么执行?是再创建一张表么?
如果rowid是你表的主键的话:
mysql、sqlserver等可以采用主键自动生成策略;闭氏
oracle使用sequence;
如果答歼rowid只针对oracle的话:
rowid是代表的是清态冲记录的物理地址
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