Introduction I just wanted to write a small and light control to arrange several controls on groups, saving space on the form. I really liked the MS Messenger�s way to group actions and contacts, so I decided to emulate its look and feel.
Contents 2 Overview 3 Preferences vs. Policy Settings 4 Group Policy Preference Items 7 Windows Settings 8 Control Panel Settings 11 Group Policy Preferences Features 17 Common Options 17 Targeting Control 18 Process Variables 20 Settings Report 22
Research in group theory have resulted in a large number of books written for postgraduates in the subject, but a good introductory text is difficult to find. This book fills the gap, providing a clear and comprehensive introduction to the theory of
order by 、group by 、having的用法区别 order by 从英文里理解就是行的排序方式，默认的为升序。 order by 后面必须列出排序的字段名，可以是多个字段名。 group by 从英文里理解就是分组。必须有“聚合函数”来配合才能使用，使用时至少需要一个分组标志字段。 什么是“聚合函数”？ 像sum()、count()、avg()等都是“聚合函数” 使用group by 的目的就是要将数据分类汇总。
