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。

--方法一

--将每科前两名学生的ID取出

SELECT *

FROM STUDENTACHIEVEMENT A

WHERE STUDENTID IN (SELECT TOP 2 STUDENTID

                       FROM STUDENTACHIEVEMENT B

                      WHERE B.COURSEID = A.COURSEID

                      ORDER BY B.ACHIEVEMENT DESC)

ORDER BY A.COURSEID, A.ACHIEVEMENT DESC

--方法二

--以科目，按成绩给记录编号，然后取出编号<=2的，就是每科前两名

SELECT *

FROM STUDENTACHIEVEMENT A

WHERE (SELECT COUNT(*)

          FROM STUDENTACHIEVEMENT B

         WHERE B.COURSEID = A.COURSEID

           AND B.ACHIEVEMENT >= A.ACHIEVEMENT) <= 2

ORDER BY A.COURSEID, A.ACHIEVEMENT DESC