SELECTA.student_id AS 学号,sw AS 生物,wl AS 物理
FROM(SELECTstudent_id,num AS swFROMscoreLEFT JOIN course ON score.course_id = course.cidWHEREcourse.cname = '生物') AS A
LEFT JOIN (SELECTstudent_id,num AS wlFROMscoreLEFT JOIN course ON score.course_id = course.cidWHEREcourse.cname = '物理'
) AS B ON A.student_id = B.student_id
WHEREsw >
IF (isnull(wl), 0, wl);

SELECT student_id,avg(num) FROM score
LEFT JOIN course
ON score.student_id=course.cid
GROUP BY student_id
HAVING avg(num)>60

SELECTstudent_id,sname,count(student_id),sum(num)
FROMscore LEFT JOIN student ON score.student_id = student.sid
GROUP BY student_id

SELECT count(tid) FROM teacher
WHERE tname LIKE '李%'

SELECT sid,sname FROM student
WHERE sid not IN(SELECT student_id FROM (SELECT cid,teacher_id,student_id,course_idFROM score LEFT JOIN course ON score.course_id=course.cid ) AS A LEFT JOIN teacher ON A.teacher_id=teacher.tid where teacher.tname='李平老师'  GROUP BY student_id
)

SELECT student.sid,student.sname FROM
(SELECT student_id,count(student_id) FROM score LEFT JOIN course ON score.course_id=course.cid  WHERE course.cid='001' or course.cid='002' GROUP BY student_id HAVING count(student_id)>1 ) AS A
LEFT JOIN student ON A.student_id=student.sid;

SELECT student_id,sname FROM
(SELECT student_id FROM score
WHERE course_id IN
(SELECT cid FROM teacher LEFT JOIN course ON teacher.tid=course.teacher_id WHERE tname='李平老师')
GROUP BY student_id
) AS B
LEFT JOIN student
ON B.student_id=student.sid

SELECT student_id,sname FROM
(SELECT A.student_id FROM
(SELECT student_id,num FROM score WHERE course_id=001) AS A
LEFT JOIN
(SELECT student_id,num FROM score WHERE course_id=002) AS B
ON A.student_id=B.student_id
WHERE A.num>B.num) AS C
LEFT JOIN student
ON C.student_id=student.sid

SELECT sid,sname FROM student WHERE sid IN
(SELECT student_id FROM score WHERE num<60 GROUP BY student_id)

SELECT sid,sname FROM student WHERE sid not IN
(SELECT student_id
FROM score
GROUP BY student_id HAVING count(course_id) = (SELECT count(cid) FROM course))

SELECT student_id,sname FROM student LEFT JOIN score ON score.student_id=student.sid
WHERE course_id in (SELECT course_id FROM score WHERE student_id=001) AND student_id != 001
GROUP BY student_id

DELETE FROM score WHERE course_id IN
(SELECT cid FROM course LEFT JOIN teacher ON course.teacher_id=teacher.tid WHERE tname='叶平老师')

select sc.student_id,(select num from score left join course on score.course_id = course.cid where course.cname = "生物" and score.student_id=sc.student_id) as sy,(select num from score left join course on score.course_id = course.cid where course.cname = "物理" and score.student_id=sc.student_id) as wl,(select num from score left join course on score.course_id = course.cid where course.cname = "体育" and score.student_id=sc.student_id) as ty,count(sc.course_id),avg(sc.num)from score as scgroup by student_id desc

SELECT course_id,max(num) as 最高分,min(num) as 最低分
FROM score
GROUP BY course_id

SELECT course_id,avg(num),teacher.tname FROM score LEFT JOIN course ON score.course_id=course.cid LEFT JOIN teacher ON course.teacher_id=teacher.tid
GROUP BY course_id
ORDER BY avg(num) DESC

SELECT course_id,count(student_id) FROM score
GROUP BY course_id

SELECT student_id,student.sname FROM score LEFT JOIN student ON score.student_id=student.sid
GROUP BY student_id
HAVING count(student_id)=1

SELECT (SELECT count(1) FROM student WHERE gender='男') AS 男,(SELECT count(1) FROM student WHERE gender='女') As 女

SELECT * FROM score LEFT JOIN
(SELECT course_id,(SELECT num FROM score WHERE score.course_id=A.course_id ORDER BY num DESC LIMIT 0,1) AS '第一名',(SELECT num FROM score WHERE score.course_id=A.course_id ORDER BY num DESC LIMIT 1,1) AS '第二名'
FROM score AS A
GROUP BY course_id) AS B
ON score.course_id=B.course_id