]]>inner join,left out join,right out join三者的不同用法Q{载) http://www.aygfsteel.com/Johnny-Ajun/archive/2011/08/28/357448.htmlHukinHukinSun, 28 Aug 2011 10:31:00 GMThttp://www.aygfsteel.com/Johnny-Ajun/archive/2011/08/28/357448.htmlhttp://www.aygfsteel.com/Johnny-Ajun/comments/357448.htmlhttp://www.aygfsteel.com/Johnny-Ajun/archive/2011/08/28/357448.html#Feedback0http://www.aygfsteel.com/Johnny-Ajun/comments/commentRss/357448.htmlhttp://www.aygfsteel.com/Johnny-Ajun/services/trackbacks/357448.html jion语句可以用来l合两个表中的记录,只要在公共字D之中有相符的值即?该语句联合两个表查询得到的结果是可以d新的数据Q可以把它看成将两个h相关内容的表联接在一h生成的表Q而一般的select 语句没有q个功能?nbsp; 阅读全文
]]>mysql中的where和having子句的区?/title>http://www.aygfsteel.com/Johnny-Ajun/archive/2011/08/28/357445.htmlHukinHukinSun, 28 Aug 2011 09:12:00 GMThttp://www.aygfsteel.com/Johnny-Ajun/archive/2011/08/28/357445.htmlhttp://www.aygfsteel.com/Johnny-Ajun/comments/357445.htmlhttp://www.aygfsteel.com/Johnny-Ajun/archive/2011/08/28/357445.html#Feedback2http://www.aygfsteel.com/Johnny-Ajun/comments/commentRss/357445.htmlhttp://www.aygfsteel.com/Johnny-Ajun/services/trackbacks/357445.html http://hi.baidu.com/ww999/blog/item/f330c8d3073107d0a8ec9a72.htmlwwhttp://hi.baidu.com/ww999/blog/item/f330c8d3073107d0a8ec9a72.htmlmysql中的where和having子句都可以实现过滤记录的功能,但他们的用法q是有一些区别的,看一例子:
用group by和having子句联合来查Z重复的记?sql如下:
select uid,email,count(*) as ct from `edm_user081217` GROUP BY email
然后看这个,容易理解了
select uid,email,count(*) as ct from `edm_user081217` GROUP BY email HAVING ct > 1
先用group by 对emailq行分组,在用having来过滤大??q样查找出来的就是重复的记录? 阅读全文