【MySQL——多表查询练习】
一、加载导入数据库
二、检索数据练习
1.查询出20070102号学生所选修课程的课程号和成绩.
SELECT stu.stuid,couid,score
FROM stu
JOIN scores ON stu.stuid=scores.stuid
WHERE stu.stuid=20070102;
2.查询出20070102号学生的学号,姓名,性别,所选修的课程名,成绩.
SELECT stu.stuid,stuname,sex,couname,score
FROM stu JOIN scores ON stu.stuid=scores.stuid
JOIN course ON scores.couid=course.couid
WHERE stu.stuid=20070102;
3.查询出选修了‘英语’课程的学生学号、姓名.
SELECT stu.stuid,stuname
FROM stu JOIN scores ON stu.stuid=scores.stuid
JOIN course ON scores.couid=course.couid
WHERE couname=“英语”;
4.查询出“电子信息系”所有学生的学号、姓名、以及选修的课程名及成绩
SELECT stu.stuid,stuname,couname,score
FROM course JOIN scores ON course.couid=scores.couid
JOIN stu ON scores.stuid=stu.stuid
JOIN dep ON stu.depid=dep.depid
WHERE depname=“电子信息系”;
5.查询出所有学生的学号、姓名、以及选修的课程名及成绩.
SELECT stu.stuid,stuname,couname,score
FROM course JOIN scores ON course.couid=scores.couid
JOIN stu ON scores.stuid=stu.stuid
JOIN dep ON stu.depid=dep.depid;
6.查询 “电子信息系”且选修了“高等数学”课程的学生的学号、姓名及成绩。
SELECT stu.stuid,stuname,score
FROM course JOIN scores ON course.couid=scores.couid
JOIN stu ON scores.stuid=stu.stuid
WHERE depid=1001 AND couname=“高等数学”;
7.统计各个系的学生人数
SELECT depname,COUNT(*)
FROM stu JOIN dep ON stu.depid=dep.depid
GROUP BY dep.depid;
8.统计各门课程的平均分
SELECT couname,AVG(score)
FROM course JOIN scores ON course.couid=scores.couid
GROUP BY couname;
9.查询各个系各门课程的平均成绩
SELECT depname,couname,AVG(score)
FROM course JOIN scores ON course.couid=scores.couid
JOIN stu ON scores.stuid=stu.stuid
JOIN dep ON stu.depid=dep.depid
GROUP BY depname,couname;
10.查找选修的课程中超过2门成绩在80分以上的学生的学号和成绩高于80分的门数
SELECT stu.stuid,COUNT(score>80)
FROM stu JOIN scores ON stu.stuid=scores.stuid
WHERE score>80
GROUP BY stu.stuid
HAVING count(couid)>2;
11.查询出三好生的候选人学号，三好生候选人需要满足的条件是：其各科平均成绩不低于85分且没有不及格的科目
SELECT stu.stuid
FROM stu JOIN scores ON stu.stuid=scores.stuid
WHERE score>60
GROUP BY couid
HAVING AVG(score)>=85;
12.求“英语”课程的平均成绩
SELECT AVG(score)
FROM course JOIN scores ON course.couid=scores.couid
WHERE couname=“英语”
GROUP BY couname;
13.查询出一门课程都没有选修的学生学号和姓名
SELECT stu.stuid,stuname
FROM stu JOIN scores ON stu.stuid=scores.stuid
WHERE couid NOT IN
(SELECT DISTINCT couid FROM scores);
14.请查询出没有学生选修的课程号和课程名
SELECT course.couid,couname
FROM course JOIN scores ON course.couid=scores.couid
WHERE course.couid NOT IN
(SELECT couid FROM course);
以上仅为个人练习操作，如有错误欢迎指正！！！