SQL第十一章 上机练习2

上机练习2
  查询每学期学时数超过50的课程数
  SELECT COUNT(*) AS 学时超过50,GradeId AS 年级 FROM Subject WHERE ClassHour>=50 GROUP BY GradeId
  查询每学期学生的平均年龄
  SELECT AVG(DATEDIFF(dd,BornDate,GETDATE())/365) AS 平均年龄,GradeId AS 年级 FROM Student GROUP BY GradeId
  查询北京地区的每学期学生人数
  SELECT COUNT(*) AS 北京总人数,GradeId AS 年级 FROM Student WHERE Address LIKE '%北京%' GROUP BY GradeId
  查询参加考试的学生中,平均分及格的学生记录,并成绩降序
  SELECT AVG(StudentResult) AS 平均分,StudentNo AS 学号 FROM Result GROUP BY StudentNo HAVING AVG(StudentResult)>=60 ORDER BY AVG(StudentResult) DESC
  查询考试日期为2013年3月22日的课的及格平均分
  SELECT AVG(StudentResult)AS 及格平均分,SubjectId AS 课程 FROM Result WHERE StudentResult>=60 AND ExamDate='2013-3-22'GROUP BY SubjectId
  查询至少一次考试不及格的学生学号,不及格次数
  SELECT StudentNo AS 学号,COUNT(*) AS 不及格次数 FROM Result WHERE StudentResult<60 GROUP BY StudentNo