所以大於六十分的
SELECT * from score where num > 60;

所有老師以及所教課程

select teacher.tname, course.cname from course
left join teacher on course.teacher_id = teacher.tid;

男生個數以及女生個數

select gender,count(gender) from student group by gender;

臨時表-在內存中臨時存在

select sid from (select * from score where num > 60)as B;

查詢生物比物理課成績高的所有學生學號

查詢平均成績大於60的同學的學號和平均成績

select student_id,avg(num) from score group by student_id having avg(num) > 60;

查詢平均成績大於60的同學的學號和平均成績和姓名

select student.sname,b.student_id,b.ccc from (select student_id,avg(num) as ccc from score group by student_id having avg(num) > 60) as b
left join student on student.sid = b.student_id; 註意聚合函數

查詢所有同學的學號，姓名，選課數，總成績；

select student_id,student.sname,count(course_id),sum(num) from score left join student on score.student_id = student.sid
group by student_id;

sql四十題