1、表架构

student(sid,sname,sage,ssex) 学生表 
course(cid,cname,tid) 课程表 
sC(sid,cid,score) 成绩表 
teacher(tid,tname) 教师表

2、建表sql语句

 

CREATE TABLE student 
  ( 
     sid INT PRIMARY KEY NOT NULL,
     sname VARCHAR(30), 
     sage INT, 
     ssex VARCHAR(8) 
  )  
 
CREATE TABLE course 
  ( 
     cid INT PRIMARY KEY NOT NULL, 
     cname VARCHAR(30), 
     tid INT 
  ) 
 
CREATE TABLE sc 
  ( 
     sid INT NOT NULL, 
     cid INT NOT NULL, 
     score INT 
  )  
 
CREATE TABLE teacher 
  ( 
     tid INT PRIMARY KEY NOT NULL, 
     tname VARCHAR(30) 
  )

 

3、问题：
（1）查询“30001”课程的所有学生的学号与分数； 

SELECT sid,score FROM sc WHERE cid="30001"

 

（2）查询“001”课程比“002”课程成绩高的所有学生的学号与分数；

SELECT a.sid,a.score FROM (SELECT sid,score FROM sc WHERE cid="30001") a,

      (SELECT sid,score FROM sc WHERE cid="30002") b

     WHERE a.score>b.score AND a.sid=b.sid

 

（3）查询平均成绩大于60分的同学的学号和平均成绩；

SELECT sid,AVG(score)

FROM sc

GROUP BY sid HAVING AVG(score)>60

 

（4）查询所有同学的学号、姓名、选课数、总成绩

SELECT s.sid AS "学号", s.sname AS "姓名", COUNT(sc.cid) AS "课程数目", SUM(sc.score) AS "总分数"

FROM student s, sc sc

WHERE s.sid=sc.sid

GROUP BY s.sid

 

（5）查询姓“李”的老师的个数；

select count(distinct(Tname))

  from teacher

  where tname like '李%';

 

（6）查询学过“张三”老师课的同学的学号、姓名

SELECT s.sid AS "学号", s.sname AS "姓名"

FROM student s, sc sc, course c, teacher t

WHERE s.sid=sc.sid AND c.cid=sc.cid AND t.tid=c.tid AND t.tname="张三"

（7）查询没有学过“张三”老师课的同学的学号、姓名

SELECT s.sid, s.sname

FROM student s

WHERE s.sid NOT IN (

SELECT s.sid

FROM student s, sc sc, course c, teacher t

WHERE s.sid=sc.sid AND c.cid=sc.cid AND t.tid=c.tid AND t.tname="张三"

)

（8）查询学过“30001”并且也学过编号“30002”课程的同学的学号、姓名 

SELECT s.sid, s.sname

FROM student s, sc sc

WHERE s.sid=sc.sid AND sc.cid="30001" AND EXISTS(

     SELECT * FROM sc AS sc2 WHERE sc2.sid=sc.sid AND sc2.cid="30002"

)

（9）查询学过“叶平”老师所教的所有课的同学的学号、姓名；

SELECT sid, sname

FROM student

WHERE sid IN (

SELECT sc.sid

FROM sc sc, course c, teacher t

WHERE sc.cid=c.cid AND c.tid=t.tid AND t.tname="张二"

)

（10）查询所有课程成绩小于60分的同学的学号、姓名

SELECT sid, sname FROM student

WHERE sid NOT IN (

SELECT DISTINCT(sc.sid) FROM student s, sc sc

WHERE sc.sid=s.sid AND sc.score>60)

 

（11）查询没有学全所有课的同学的学号、姓名；

SELECT sid, sname FROM student 

WHERE sid NOT IN(

SELECT s.sid FROM student s, sc sc

WHERE sc.sid=s.sid

GROUP BY s.sid

HAVING COUNT(sc.cid)=(

SELECT COUNT(cid) FROM course))

（12）查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分

SELECT cid AS "课程ID", MAX(score) AS "最高分", MIN(score) AS "最低分"
FROM sc
GROUP BY cid

（13）按各科平均成绩从低到高和及格率的百分数从高到低顺序

(方式一)
SELECT sc.cid AS "课程ID",c.cname AS "课程名", AVG(sc.score) AS "平均成绩",
SUM(CASE WHEN sc.score > 60 THEN 1 ELSE 0 END)/COUNT(1)*100 AS "及格百分数"
FROM sc sc, course c
WHERE sc.cid=c.cid
GROUP BY sc.cid
ORDER BY AVG(sc.score) ASC,
SUM(CASE WHEN sc.score > 60 THEN 1 ELSE 0 END)/COUNT(1)*100 DESC


(方式二)
SELECT sc.cid AS "课程ID",c.cname AS "课程名", IFNULL(AVG(sc.score),0) AS "平均成绩",
100*SUM(CA