SQL__数据查询语句__分组查询

SQL__数据查询语句__排列__分组

1.Order by—按指定方法进行排序（ order by 后面可接很多列名，也可以只有一个列名 ）

• 举例说明

  
  	------以下两个查询查询的是相同的内容（一个包含了having(),一个包含了all）-------------
  	select Title,Vacations=SUM(VacationHours)
  	from HumanResources.Employee
  	where Title in('Recruiter','Stocker','DesignEngnieer')
  	Group by all Title                                ------使用了all，就默认显示全部内容（包括空值）
  	having SUM(Vacationhours) is  not null                         
  	ORder by SUM(Vacationhours) desc
  	
  	select Title,Vacations=SUM(VacationHours)
  	from HumanResources.Employee
  	where Title in('Recruiter','Stocker','DesignEngnieer')
  	Group by Title                                    -------没用all，就默认删除了NUll的部分          
  	ORder by SUM(Vacationhours) desc
  	
  

2.desc 等价于 descending order 简称倒序排列

• 例子如下

  
  	select [SalesOrderDetailID],[UnitPrice],[ModifiedDate],[SalesOrderID]
  	from Sales.SalesOrderDetail
  	where [UnitPrice]>2000 and [SalesOrderDetailID]<10
  	order by [UnitPrice] desc
  	
  

3.asc 等价于 ascending order 简称正序排列

• 例子如下

  
  	select [SalesOrderDetailID],[UnitPrice],[ModifiedDate],[SalesOrderID]
  	from Sales.SalesOrderDetail
  	where [UnitPrice]>2000 and [SalesOrderDetailID]<10
  	order by 2 asc---因为[UnitPrice在select后是第二个列---
  	-----偷懒的方法：order by + 数字
  	
  	select [SalesOrderDetailID],[UnitPrice],[ModifiedDate],[SalesOrderID]
  	from Sales.SalesOrderDetail
  	where [UnitPrice]>2000 and [SalesOrderDetailID]<10
  	order by [UnitPrice],[SalesOrderDetailID] asc
  	
  

4.升降序排列之 desc – asc

• 例子如下

  
  	select GroupName,DepartmentID,Name
  	from Humanresources.Department 
  	order by GroupName,DepartmentID desc 
  	
  	select GroupName,DepartmentID,Name
  	from Humanresources.Department 
  	order by GroupName,DepartmentID asc
  
  

5.补充

注意： 由于where（）没有having（）的一部分功能。所以，当出现聚合函数，要对其进行限定时，都用having（），也只能用having.