摘要：access：select top (10) * from table1 where 1=1db2：select column from table where 1=1 fetch first 10 rows onlymysql：select * from table1 where 1=1 limi... 阅读全文

摘要：where和having子句都可以实现过滤记录的功能,但他们的用法还是有一些区别的,看一例子:用group by和having子句联合来查出不重复的记录,sql如下:select uid,email,count(*) as ct from `edm_user081217` GROUP BY email然后看这个，就容易理解了select uid,email,count(*) as ct from `edm_user081217` GROUP BY email HAVING ct > 1先用group by 对email进行分组,在用having来过滤大于1的,这样查找出来的就是重复的记录 阅读全文