SQL语句

1.在SQL   Server   数据库中，有一个表StudentAchievement（学生成绩）,它有三个字段：StudentID(varchar(8),学生编号)，CourseID(varchar(10),课程编号)，Achievement(int   ，成绩)，写一条SQL语句，筛选出每门课程的前两名的学生编号，课程编号，成绩并排序。
Select   *  
  From   StudentAchievement   a  
  Where   StudentID   in   (Select   Top   2   StudentID    
                                          From   StudentAchievement  
                                          Where   CourseID=a.CourseID    
                                          Order   by   Achievement   desc)  
  order   by   CourseID,Achievement   desc

2.有倆個表；表Student(UserID,UserName),UserID為主鍵，表SourceInfo(UserID,SourceID,Source)，無主鍵
 
要求：查詢出選擇三門課以上的Username，UserID

select a.username,a.userid,Count(1) as SourceIDCount from userinfo as a with(nolock)
join SourceInfo as b with(nolock) On a.UserID =b.UserID
group by a.username,a.userid
having Count(1) >=3
--having 表示group by 后的筛选