第三章的小知识点-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_36074157/article/details/54234391

本文演示了如何在SQL中声明变量并进行简单的数据查询操作。包括基本的数据类型定义，如nvarchar、decimal和datetime等，并展示了如何使用这些变量进行字符串拼接及参与查询条件。此外，还提供了一个具体的例子，通过查询某个科目的平均分来筛选出成绩优秀的前三名学生。

declare @name nvarchar(32)
set @name='网'
print @name
      
declare @balance decimal(18,7)
set @balance=3.1415926
print @balance

declare @birthday datetime
set @birthday='2001-5-29'
print @birthday
--------------------------------------------
declare @num int
set @num=5
print 'num value is'+cast(@num as nvarchar(32))

declare @nu int 
set @nu=5
print 'nu value is'+convert(nvarchar(32),@nu)
----------------------------------------------
select * from Result
--order by examdate
--编号
declare @subid int
select @subid-SubjectId from dbo.Subject
Where SubjectName='oop'
--平均分
declare @avg int
select @avg=avg(StudentResult) from dbo.Subject
Where examdate>='2013-08-09' and examdate <'2013-08-10'
and SubjectId=@subid

 --前三名的成绩
if(@avg>=70)
  begin
  print '成绩优秀'
  select top 3 * from Result
  Where examdate>='2013-08-09' and examdate <'2013-08-10' and SubjectId=@subid
  order by StudentResult desc
end

if(@avg>=70)
  begin
  print '成绩优秀'
  select top 3 * from Result
  Where examdate>='2013-08-09' and examdate <'2013-08-10' and SubjectId=@subid
  order by StudentResult desc
end