MySQL与Oracle中分组、聚合函数的区别

yehui之中期回顾 2010-01-19

今天需要这样一句sql:先用group by进行分组,然后利用聚合函数count 或者sum进行计算,并显示其它的辅助信息。

在MySQL环境中,我模拟如下环境:

CREATE TABLE `room` (                    

          `rid` varchar(5) default NULL,         

          `rname` varchar(5) default NULL,       

          `pid` int(11) default NULL,            

          `seq` int(11) NOT NULL auto_increment, 

          PRIMARY KEY  (`seq`)                   

        ) ENGINE=InnoDB DEFAULT CHARSET=utf8  
 房间表,seq房间入住序号(主键),rname为房间名,这里不考虑第三范式

情景:人住房间,

统计某个房间某个人住的次数

 

用户表,客人的信息
 
CREATE TABLE `user1` (                  

          `ID` int(11) NOT NULL auto_increment, 

          `USERNAME` varchar(50) default '',    

          `PASSWORD` varchar(50) default '',    

          PRIMARY KEY  (`ID`)                   

        ) ENGINE=InnoDB DEFAULT CHARSET=gbk
 

Mysql中语句如下:

select count(u.username),r.rname,r.rid,r.pid

from room r,user1 u

where r.pid=u.id

group by r.rid,r.pid

这里r.rname并没有出现在group by子句、聚合函数中,但是MYSQL中仍然能够执行、列出数据。
 
但是,在Oracle中,却不能!!!!
 
Oracle环境中:

/*

 --显示:Ora-00979 not a ORDER BY expression

 --因为: order by 后边的c.channel_code不在ORDER BY子句中

 select count(c.channel_name),m.media_name

  from channel c,media m

  where c.media_code = m.media_code

 group by c.media_code,m.media_name

 order by c.channel_code

 

--显示:Ora-00979 not a GROUP BY expression

--因为:group by 或者聚合函数中没有包含c.channel_name

 select count(c.channel_name),m.media_name,c.channel_name

  from channel c,media m

  where c.media_code = m.media_code

 group by c.media_code,m.media_name

  */

--通过:

select count(c.channel_name),m.media_name

  from channel c,media m

  where c.media_code = m.media_code

 group by m.media_name

--正常

select count(c.channel_name),m.media_name

  from channel c,media m

  where c.media_code = m.media_code

 group by c.media_code,m.media_name

 

--正常

select count(c.channel_code),m.media_name

  from channel c,media m

  where c.media_code = m.media_code

 group by c.media_code,m.media_name

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