此笔记为听柠檬班公开课后笔记，特为其打call，如有侵权，请随时联系我删帖哦～

课堂习题及课后题

建表语句

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;-- ----------------------------
-- Table structure for course
-- ----------------------------
DROP TABLE IF EXISTS `course`;
CREATE TABLE `course`  (`Cno` int(11) NOT NULL COMMENT '课程编号',`Cname` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '课程名称',`Tno` int(11) NULL DEFAULT NULL COMMENT '老师编号',PRIMARY KEY (`Cno`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;-- ----------------------------
-- Records of course
-- ----------------------------
INSERT INTO `course` VALUES (1, '数学', 1);
INSERT INTO `course` VALUES (2, '语文', 2);
INSERT INTO `course` VALUES (3, '英文', 1);-- ----------------------------
-- Table structure for sc
-- ----------------------------
DROP TABLE IF EXISTS `sc`;
CREATE TABLE `sc`  (`Sno` int(11) NOT NULL COMMENT '学号',`Cno` int(11) NOT NULL COMMENT '课程编号',`score` int(255) NULL DEFAULT NULL COMMENT '分数',PRIMARY KEY (`Sno`, `Cno`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;-- ----------------------------
-- Records of sc
-- ----------------------------
INSERT INTO `sc` VALUES (1, 1, 99);
INSERT INTO `sc` VALUES (1, 2, 80);
INSERT INTO `sc` VALUES (1, 3, 50);
INSERT INTO `sc` VALUES (2, 1, 70);
INSERT INTO `sc` VALUES (2, 2, 90);
INSERT INTO `sc` VALUES (3, 1, 90);
INSERT INTO `sc` VALUES (4, 1, 60);
INSERT INTO `sc` VALUES (4, 2, 50);
INSERT INTO `sc` VALUES (4, 3, 40);-- ----------------------------
-- Table structure for student
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student`  (`Sno` int(255) NOT NULL COMMENT '学号',`Sname` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '姓名',`Sage` int(255) NULL DEFAULT NULL COMMENT '年龄',`Ssex` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '性别',PRIMARY KEY (`Sno`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `student` VALUES (1, '张三丰', 108, '男');
INSERT INTO `student` VALUES (2, '李小龙', 20, '男');
INSERT INTO `student` VALUES (3, '小龙女', 17, '女');
INSERT INTO `student` VALUES (4, '白发魔女', 18, '女');
INSERT INTO `student` VALUES (5, '韦小宝', 19, '男');-- ----------------------------
-- Table structure for teacher
-- ----------------------------
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher`  (`Tno` int(11) NOT NULL COMMENT '老师编号',`Tname` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '老师名称',PRIMARY KEY (`Tno`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;-- ----------------------------
-- Records of teacher
-- ----------------------------
INSERT INTO `teacher` VALUES (1, '无崖子');
INSERT INTO `teacher` VALUES (2, '孤独求败');
INSERT INTO `teacher` VALUES (3, '洪七公');SET FOREIGN_KEY_CHECKS = 1;

表

课后题

1 查询年龄小于18岁的学员信息
2 查询无崖子授课信息
3 查询没有参与任意课程的学生信息
4 查询无崖子每个授课课程的学员人数
5 查询张三丰数学成绩
6 查询出语文最高分
7 查询没有参与语文考试的学生信息
8 查询语数外三门成绩的平均分
9 查询报名孤独求败老师课程的学生信息
10 没有报名孤独求败老师课程的学生信息

解答及思路

#1 查询年龄小于18岁的学员信息
SELECT * FROM student WHERE student.sage < 18;#2 查询无崖子授课信息
SELECT * FROM teacher AS tr
INNER JOIN course AS ce ON tr.Tno = ce.Tno
WHERE tr.Tname = '无崖子';
#也可如下，结果无其他不需要的信息
SELECT tr.Tname, ce.Cname FROM teacher AS tr
INNER JOIN course AS ce ON tr.Tno = ce.Tno
WHERE tr.Tname = '无崖子';#3 查询没有参与任意课程的学生信息
SELECT * FROM student AS st
LEFT JOIN sc ON st.Sno = sc.Sno
WHERE sc.Sno IS NULL;#有想过用sc.score,但是觉得没sc.Sno好，这是唯一索引，不容易出错
#思路：学生表和课程表没有关联关系；没有成绩可以认为没有参加课程，所以聚焦在学生表和成绩表#4 查询无崖子每个授课课程的学员人数
SELECT tr.Tname, ce.Cname, COUNT(*) FROM teacher AS tr
LEFT JOIN course AS ce ON tr.Tno = ce.Tno
LEFT JOIN sc on ce.Cno = sc.Cno
WHERE tr.Tname = '无崖子'
GROUP BY ce.Cno;
#如下是老师的答案
select c.Cno,c.Cname,count(*) from teacher d
INNER JOIN course c on d.Tno = c.Tno
INNER JOIN sc b on b.Cno = c.Cno
where d.TName = '无崖子'
GROUP BY c.Cno,c.Cname;#5 查询张三丰数学成绩
SELECT st.Sname, ce.Cname, sc.score FROM student AS st
INNER JOIN sc on st.Sno = sc.Sno
INNER JOIN course AS ce on sc.Cno = ce.Cno
WHERE st.Sname = '张三丰' AND ce.Cname = '数学';
#LEFT JOIN也OK#6 查询出语文最高分
SELECT ce.Cname, sc.score FROM course AS ce
INNER JOIN sc ON ce.Cno = sc.Cno
WHERE ce.Cname = '语文'
ORDER BY sc.score DESC LIMIT 1;
#LEFT JOIN也OK
SELECT ce.Cname, sc.score FROM course AS ce
LEFT JOIN sc ON ce.Cno = sc.Cno
WHERE ce.Cname = '语文'
ORDER BY sc.score DESC LIMIT 1;
#ASC升序，由小到大；DESC降序，由大到小；
#可以用MAX()
SELECT ce.Cname, MAX(sc.score) AS max_score FROM course AS ce
INNER JOIN sc ON ce.Cno = sc.Cno AND ce.Cname = '语文' #用 INNER JOIN更合适，LEFT JOIN会查出无用信息
GROUP BY ce.Cname #7 查询没有参与语文考试的学生信息
SELECT * FROM student AS st
LEFT JOIN sc ON st.Sno = sc.Sno
LEFT JOIN course AS ce ON sc.Cno = ce.Cno
WHERE ce.Cname = '语文' AND sc.Sno IS NULLSELECT st.Sname, se.Cname, se.Sno FROM student AS st
LEFT JOIN
(SELECT ce.Cname, sc.Sno, sc.score FROM course AS ceLEFT JOIN sc ON sc.Cno = ce.Cno AND ce.Cname = '语文') AS se #先查语文课程的所有成绩
ON st.Sno = se.Sno #再查每一个学生对应的语文成绩
WHERE se.Sno IS NULL #当这个学生没有语文成绩，就意味着他没考试；Sno为唯一索引，所以可以当该索引为空时；
#老师答案如下，思路一致，用了右连接：
select * from course c
INNER JOIN sc b on c.Cno = b.Cno and c.Cname = '语文'
RIGHT JOIN Student a on a.Sno = b.Sno
where b.Sno is null;
# 和学生做外连接#8 查询语数外三门成绩的平均分
SELECT ce.Cname, AVG(sc.score) AS avg_score FROM course AS ce
LEFT JOIN sc ON ce.Cno = sc.Cno
GROUP BY ce.Cname#9 查询报名孤独求败老师课程的学生信息
SELECT * FROM teacher AS tr #用*，尤其连了四表，会出现很多重复字段，所以查询时可以写好要显示哪些字段，如下段
INNER JOIN course AS ce ON tr.Tno = ce.Tno AND tr.Tname = '孤独求败' #此处用左连接会显示所有老师，除非最后加上where老师名字是孤独求败
LEFT JOIN sc on ce.Cno = sc.Cno
LEFT JOIN student AS st ON sc.Sno = st.Sno
#接第一行：
SELECT tr.Tname, ce.Cname, st.Sname FROM teacher AS tr
INNER JOIN course AS ce ON tr.Tno = ce.Tno AND tr.Tname = '孤独求败'
LEFT JOIN sc on ce.Cno = sc.Cno
LEFT JOIN student AS st ON sc.Sno = st.Sno#10 没有报名孤独求败老师课程的学生信息
#思路：同没有参加语文考试的学生题思路一致；
#先查询孤独求败老师的所有课程信息，再和学生做外连，看哪个学生没有课程信息就是没参加孤独求败老师的课程
#只有成绩表和学生表有Sno关联，所以要和学生表关联先得关联成绩表
SELECT tr.Tname, ce.Cname, st.Sname FROM teacher AS tr
INNER JOIN course AS ce ON tr.Tno = ce.Tno AND tr.Tname = '孤独求败'
INNER JOIN sc ON ce.Cno = sc.Cno
RIGHT JOIN student AS st ON sc.Sno = st.Sno
WHERE sc.Sno IS NULL

心得不写，下次忘了，我就再敲一遍，哈哈哈哈哈哈哈哈

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【MySQL】听柠檬班公开课后，学习笔记及作业（二）

课堂习题及课后题

建表语句

表

课后题

解答及思路

心得不写，下次忘了，我就再敲一遍，哈哈哈哈哈哈哈哈

【MySQL】听柠檬班公开课后，学习笔记及作业（二）相关推荐

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