python之数据库

'''
# 作业内容
1、查询所有的课程的名称以及对应的任课老师姓名

2、查询学生表中男女生各有多少人

3、查询物理成绩等于100的学生的姓名

4、查询平均成绩大于八十分的同学的姓名和平均成绩

5、查询所有学生的学号，姓名，选课数，总成绩

6、 查询姓李老师的个数

7、 查询没有报李平老师课的学生姓名

8、 查询物理课程比生物课程高的学生的学号

9、 查询没有同时选修物理课程和体育课程的学生姓名

10、查询挂科超过两门(包括两门)的学生姓名和班级
'''

博客链接：https://blog.51cto.com/11019859/2074536

# 创建库和库表，并插入数据
'''
班级表：class
课程表：course
成绩表：score
学生表：student
老师表：teacher
'''

Mysql> create database sqlexam;
Query OK, 1 row affected (0.01 sec)

mysql> use sqlexam
Database changed
mysql>
mysql> SET NAMES utf8;
Query OK, 0 rows affected (0.01 sec)

mysql> SET FOREIGN_KEY_CHECKS = 0;
Query OK, 0 rows affected (0.00 sec)

mysql> DROP TABLE IF EXISTS `class`;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> CREATE TABLE `class` (
    ->   `cid` int(11) NOT NULL AUTO_INCREMENT,
    ->   `caption` varchar(32) NOT NULL,
    ->   PRIMARY KEY (`cid`)
    -> ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.04 sec)

mysql> INSERT INTO `class` VALUES ('1', '三年二班'), ('2', '三年三班'), ('3', ' 一年二班'), ('4', '二年九班');
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> DROP TABLE IF EXISTS `course`;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> CREATE TABLE `course` (
    ->   `cid` int(11) NOT NULL AUTO_INCREMENT,
    ->   `cname` varchar(32) NOT NULL,
    ->   `teacher_id` int(11) NOT NULL,
    ->   PRIMARY KEY (`cid`),
    ->   KEY `fk_course_teacher` (`teacher_id`),
    ->   CONSTRaiNT `fk_course_teacher` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`tid`)
    -> ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.04 sec)

mysql> INSERT INTO `course` VALUES ('1', '生物', '1'), ('2', '物理', '2'), ('3', '体育', '3'), ('4', '美术', '2');
Query OK, 4 rows affected (0.01 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> DROP TABLE IF EXISTS `score`;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> CREATE TABLE `score` (
    ->   `sid` int(11) NOT NULL AUTO_INCREMENT,
    ->   `student_id` int(11) NOT NULL,
    ->   `course_id` int(11) NOT NULL,
    ->   `num` int(11) NOT NULL,
    ->   PRIMARY KEY (`sid`),
    ->   KEY `fk_score_student` (`student_id`),
    ->   KEY `fk_score_course` (`course_id`),
    ->   CONSTRAINT `fk_score_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`),
    ->   CONSTRAINT `fk_score_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`)
    -> ) ENGINE=InnoDB AUTO_INCREMENT=53 DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.02 sec)

mysql> INSERT INTO `score` VALUES ('1', '1', '1', '10'), ('2', '1', '2', '9'), ('5', '1', '4', '66'), ('6', '2', '1', '8'), ('8', '2', '3', '68'), ('9', '2', '4', '99'), ('10', '3', '1', '77'), ('11', '3', '2', '66'), ('12', '3', '3', '87'), ('13', '3', '4', '99'), ('14', '4', '1', '79'), ('15', '4', '2', '11'), ('16', '4', '3', '67'), ('17', '4', '4', '100'), ('18', '5', '1', '79'), ('19', '5', '2', '11'), ('20', '5', '3', '67'), ('21', '5', '4', '100'), ('22', '6', '1', '9'), ('23', '6', '2', '100'), ('24', '6', '3', '67'), ('25', '6', '4', '100'), ('26', '7', '1', '9'), ('27', '7', '2', '100'), ('28', '7', '3', '67'), ('29', '7', '4', '88'), ('30', '8', '1', '9'), ('31', '8', '2', '100'), ('32', '8', '3', '67'), ('33', '8', '4', '88'), ('34', '9', '1', '91'), ('35', '9', '2', '88'), ('36', '9', '3', '67'), ('37', '9', '4', '22'), ('38', '10', '1', '90'), ('39', '10', '2', '77'), ('40', '10', '3', '43'), ('41', '10', '4', '87'), ('42', '11', '1', '90'), ('43', '11', '2', '77'), ('44', '11', '3', '43'), ('45', '11', '4', '87'), ('46', '12', '1', '90'), ('47', '12', '2', '77'), ('48', '12', '3', '43'), ('49', '12', '4', '87'), ('52', '13', '3', '87');
Query OK, 47 rows affected (0.01 sec)
Records: 47  Duplicates: 0  Warnings: 0

mysql> DROP TABLE IF EXISTS `student`;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> CREATE TABLE `student` (
    ->   `sid` int(11) NOT NULL AUTO_INCREMENT,
    ->   `gender` char(1) NOT NULL,
    ->   `class_id` int(11) NOT NULL,
    ->   `sname` varchar(32) NOT NULL,
    ->   PRIMARY KEY (`sid`),
    ->   KEY `fk_class` (`class_id`),
    ->   CONSTRAINT `fk_class` FOREIGN KEY (`class_id`) REFERENCES `class` (`cid`)
    -> ) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.02 sec)

mysql> INSERT INTO `student` VALUES ('1', '男', '1', '理解'), ('2', '女', '1', '钢蛋'), ('3', '男', '1', '张三'), ('4', '男', '1', '张一'), ('5', '女', '1', '张二'), ('6', '男', '1', '张四'), ('7', '女', '2', '铁锤'), ('8', '男', '2', '李三'), ('9', '男', '2', '李一'), ('10', '女', '2', '李二'), ('11', '男', '2', '李四'), ('12', '女', '3', '如花'), ('13', '男', '3', '刘三'), ('14', '男', '3', '刘 一'), ('15', '女', '3', '刘二'), ('16', '男', '3', '刘四');
Query OK, 16 rows affected (0.01 sec)
Records: 16  Duplicates: 0  Warnings: 0

mysql> DROP TABLE IF EXISTS `teacher`;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> CREATE TABLE `teacher` (
    ->   `tid` int(11) NOT NULL AUTO_INCREMENT,
    ->   `tname` varchar(32) NOT NULL,
    ->   PRIMARY KEY (`tid`)
    -> ) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.02 sec)

mysql> INSERT INTO `teacher` VALUES ('1', '张磊老师'), ('2', '李平老师'), ('3', '刘海燕老师'), ('4', '朱云海老师'), ('5', '李杰老师');
Query OK, 5 rows affected (0.00 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql> SET FOREIGN_KEY_CHECKS = 1;
Query OK, 0 rows affected (0.00 sec)

mysql> show tables;
+-------------------+
| Tables_in_sqlexam |
+-------------------+
| class             |
| course            |
| score             |
| student           |
| teacher           |
+-------------------+
5 rows in set (0.00 sec)

# 1、查询所有的课程的名称以及对应的任课老师姓名
mysql> SELECT
    ->     course.cname,
    ->     teacher.tname
    -> FROM
    ->     course
    -> INNER JOIN teacher ON course.teacher_id = teacher.tid;
+--------+-----------------+
| cname  | tname           |
+--------+-----------------+
| 生物   | 张磊老师        |
| 物理   | 李平老师        |
| 美术   | 李平老师        |
| 体育   | 刘海燕老师      |
+--------+-----------------+
4 rows in set (0.01 sec)

# 2、查询学生表中男女生各有多少人
mysql> SELECT
    ->     gender 性别,
    ->     count(1) 人数
    -> FROM
    ->     student
    -> GROUP BY
    ->     gender;
+--------+--------+
| 性别   | 人数   |
+--------+--------+
| 女     |      6 |
| 男     |     10 |
+--------+--------+
2 rows in set (0.00 sec)

# 3、查询物理成绩等于100的学生的姓名
mysql> SELECT
    ->     student.sname
    -> FROM
    ->     student
    -> WHERE
    ->     sid IN (
    ->         SELECT
    ->             student_id
    ->         FROM
    ->             score
    ->         INNER JOIN course ON score.course_id = course.cid
    ->         WHERE
    ->             course.cname = '物理'
    ->         AND score.num = 100
    ->     );
+--------+
| sname  |
+--------+
| 张四   |
| 铁锤   |
| 李三   |
+--------+
3 rows in set (0.00 sec)

# 4、查询平均成绩大于八十分的同学的姓名和平均成绩
mysql> SELECT
    ->     student.sname,
    ->     t1.avg_num
    -> FROM
    ->     student
    -> INNER JOIN (
    ->     SELECT
    ->         student_id,
    ->         avg(num) AS avg_num
    ->     FROM
    ->         score
    ->     GROUP BY
    ->         student_id
    ->     HAVING
    ->         avg(num) > 80
    -> ) AS t1 ON student.sid = t1.student_id;
+--------+---------+
| sname  | avg_num |
+--------+---------+
| 张三   | 82.2500 |
| 刘三   | 87.0000 |
+--------+---------+
2 rows in set (0.00 sec)

# 5、查询所有学生的学号，姓名，选课数，总成绩
mysql> SELECT
    ->     student.sid,
    ->     student.sname,
    ->     t1.course_num,
    ->     t1.total_num
    -> FROM
    ->     student
    -> LEFT JOIN (
    ->     SELECT
    ->         student_id,
    ->         COUNT(course_id) course_num,
    ->         sum(num) total_num
    ->     FROM
    ->         score
    ->     GROUP BY
    ->         student_id
    -> ) AS t1 ON student.sid = t1.student_id;
+-----+--------+------------+-----------+
| sid | sname  | course_num | total_num |
+-----+--------+------------+-----------+
|   1 | 理解   |          3 |        85 |
|   2 | 钢蛋   |          3 |       175 |
|   3 | 张三   |          4 |       329 |
|   4 | 张一   |          4 |       257 |
|   5 | 张二   |          4 |       257 |
|   6 | 张四   |          4 |       276 |
|   7 | 铁锤   |          4 |       264 |
|   8 | 李三   |          4 |       264 |
|   9 | 李一   |          4 |       268 |
|  10 | 李二   |          4 |       297 |
|  11 | 李四   |          4 |       297 |
|  12 | 如花   |          4 |       297 |
|  13 | 刘三   |          1 |        87 |
|  14 | 刘一   |       NULL |      NULL |
|  15 | 刘二   |       NULL |      NULL |
|  16 | 刘四   |       NULL |      NULL |
+-----+--------+------------+-----------+
16 rows in set (0.00 sec)

# 6、 查询姓李老师的个数
mysql> SELECT
    ->     count(tid)
    -> FROM
    ->     teacher
    -> WHERE
    ->     tname LIKE '李%';
+------------+
| count(tid) |
+------------+
|          2 |
+------------+
1 row in set (0.00 sec)

# 7、 查询没有报李平老师课的学生姓名
mysql> SELECT
    ->     student.sname
    -> FROM
    ->     student
    -> WHERE
    ->     sid NOT IN (
    ->         SELECT DISTINCT
    ->             student_id
    ->         FROM
    ->             score
    ->         WHERE
    ->             course_id IN (
    ->                 SELECT
    ->                     course.cid
    ->                 FROM
    ->                     course
    ->                 INNER JOIN teacher ON course.teacher_id = teacher.tid
    ->                 WHERE
    ->                     teacher.tname = '李平老师'
    ->             )
    ->     );
+--------+
| sname  |
+--------+
| 刘三   |
| 刘一   |
| 刘二   |
| 刘四   |
+--------+
4 rows in set (0.00 sec)

# 8、 查询物理课程比生物课程高的学生的学号
mysql> SELECT
    ->     t1.student_id
    -> FROM
    ->     (
    ->         SELECT
    ->             student_id,
    ->             num
    ->         FROM
    ->             score
    ->         WHERE
    ->             course_id = (
    ->                 SELECT
    ->                     cid
    ->                 FROM
    ->                     course
    ->                 WHERE
    ->                     cname = '物理'
    ->             )
    ->     ) AS t1
    -> INNER JOIN (
    ->     SELECT
    ->         student_id,
    ->         num
    ->     FROM
    ->         score
    ->     WHERE
    ->         course_id = (
    ->             SELECT
    ->                 cid
    ->             FROM
    ->                 course
    ->             WHERE
    ->                 cname = '生物'
    ->         )
    -> ) AS t2 ON t1.student_id = t2.student_id
    -> WHERE
    ->     t1.num > t2.num;
+------------+
| student_id |
+------------+
|          6 |
|          7 |
|          8 |
+------------+
3 rows in set (0.00 sec)

# 9、 查询没有同时选修物理课程和体育课程的学生姓名
mysql> SELECT
    ->     student.sname
    -> FROM
    ->     student
    -> WHERE
    ->     sid IN (
    ->         SELECT
    ->             student_id
    ->         FROM
    ->             score
    ->         WHERE
    ->             course_id IN (
    ->                 SELECT
    ->                     cid
    ->                 FROM
    ->                     course
    ->                 WHERE
    ->                     cname = '物理'
    ->                 OR cname = '体育'
    ->             )
    ->         GROUP BY
    ->             student_id
    ->         HAVING
    ->             COUNT(course_id) = 1
    ->     );
+--------+
| sname  |
+--------+
| 理解   |
| 钢蛋   |
| 刘三   |
+--------+
3 rows in set (0.00 sec)

# 10、查询挂科超过两门(包括两门)的学生姓名和班级
mysql> SELECT
    ->     student.sname,
    ->     class.caption
    -> FROM
    ->     student
    -> INNER JOIN (
    ->     SELECT
    ->         student_id
    ->     FROM
    ->         score
    ->     WHERE
    ->         num < 60
    ->     GROUP BY
    ->         student_id
    ->     HAVING
    ->         count(course_id) >= 2
    -> ) AS t1
    -> INNER JOIN class ON student.sid = t1.student_id
    -> AND student.class_id = class.cid;
+--------+--------------+
| sname  | caption      |
+--------+--------------+
| 理解   | 三年二班     |
+--------+--------------+
1 row in set (0.00 sec)

# 11、查询选修了所有课程的学生姓名
mysql> SELECT
    ->     student.sname
    -> FROM
    ->     student
    -> WHERE
    ->     sid IN (
    ->         SELECT
    ->             student_id
    ->         FROM
    ->             score
    ->         GROUP BY
    ->             student_id
    ->         HAVING
    ->             COUNT(course_id) = (SELECT count(cid) FROM course)
    ->     );
+--------+
| sname  |
+--------+
| 张三   |
| 张一   |
| 张二   |
| 张四   |
| 铁锤   |
| 李三   |
| 李一   |
| 李二   |
| 李四   |
| 如花   |
+--------+
10 rows in set (0.01 sec)

# 12、查询李平老师教的课程的所有成绩记录
mysql> SELECT
    ->     *
    -> FROM
    ->     score
    -> WHERE
    ->     course_id IN (
    ->         SELECT
    ->             cid
    ->         FROM
    ->             course
    ->         INNER JOIN teacher ON course.teacher_id = teacher.tid
    ->         WHERE
    ->             teacher.tname = '李平老师'
    ->     );
+-----+------------+-----------+-----+
| sid | student_id | course_id | num |
+-----+------------+-----------+-----+
|   2 |          1 |         2 |   9 |
|  11 |          3 |         2 |  66 |
|  15 |          4 |         2 |  11 |
|  19 |          5 |         2 |  11 |
|  23 |          6 |         2 | 100 |
|  27 |          7 |         2 | 100 |
|  31 |          8 |         2 | 100 |
|  35 |          9 |         2 |  88 |
|  39 |         10 |         2 |  77 |
|  43 |         11 |         2 |  77 |
|  47 |         12 |         2 |  77 |
|   5 |          1 |         4 |  66 |
|   9 |          2 |         4 |  99 |
|  13 |          3 |         4 |  99 |
|  17 |          4 |         4 | 100 |
|  21 |          5 |         4 | 100 |
|  25 |          6 |         4 | 100 |
|  29 |          7 |         4 |  88 |
|  33 |          8 |         4 |  88 |
|  37 |          9 |         4 |  22 |
|  41 |         10 |         4 |  87 |
|  45 |         11 |         4 |  87 |
|  49 |         12 |         4 |  87 |
+-----+------------+-----------+-----+
23 rows in set (0.00 sec)

# 13、查询全部学生都选修了的课程号和课程名
mysql> SELECT
    ->     cid,
    ->     cname
    -> FROM
    ->     course
    -> WHERE
    ->     cid IN (
    ->         SELECT
    ->             course_id
    ->         FROM
    ->             score
    ->         GROUP BY
    ->             course_id
    ->         HAVING
    ->             COUNT(student_id) = (
    ->                 SELECT
    ->                     COUNT(sid)
    ->                 FROM
    ->                     student
    ->             )
    ->     );
Empty set (0.00 sec)

# 14、查询每门课程被选修的次数
mysql> SELECT
    ->     course_id,
    ->     COUNT(student_id)
    -> FROM
    ->     score
    -> GROUP BY
    ->     course_id;
+-----------+-------------------+
| course_id | COUNT(student_id) |
+-----------+-------------------+
|         1 |                12 |
|         2 |                11 |
|         3 |                12 |
|         4 |                12 |
+-----------+-------------------+
4 rows in set (0.00 sec)

# 15、查询只选修了一门课程的学生姓名和学号
mysql> SELECT
    ->     sid,
    ->     sname
    -> FROM
    ->     student
    -> WHERE
    ->     sid IN (
    ->         SELECT
    ->             student_id
    ->         FROM
    ->             score
    ->         GROUP BY
    ->             student_id
    ->         HAVING
    ->             COUNT(course_id) = 1
    ->     );
+-----+--------+
| sid | sname  |
+-----+--------+
|  13 | 刘三   |
+-----+--------+
1 row in set (0.00 sec)

# 16、查询所有学生考出的成绩并按从高到低排序（成绩去重）
mysql> SELECT DISTINCT num FROM score ORDER BY num DESC;
+-----+
| num |
+-----+
| 100 |
|  99 |
|  91 |
|  90 |
|  88 |
|  87 |
|  79 |
|  77 |
|  68 |
|  67 |
|  66 |
|  43 |
|  22 |
|  11 |
|  10 |
|   9 |
|   8 |
+-----+
17 rows in set (0.00 sec)

#17、查询平均成绩大于85的学生姓名和平均成绩
mysql> SELECT
    ->     sname,
    ->     t1.avg_num
    -> FROM
    ->     student
    -> INNER JOIN (
    ->     SELECT
    ->         student_id,
    ->         avg(num) avg_num
    ->     FROM
    ->         score
    ->     GROUP BY
    ->         student_id
    ->     HAVING
    ->         AVG(num) > 85
    -> ) t1 ON student.sid = t1.student_id;
+--------+---------+
| sname  | avg_num |
+--------+---------+
| 刘三   | 87.0000 |
+--------+---------+
1 row in set (0.00 sec)

# 18、查询生物成绩不及格的学生姓名和对应生物分数
mysql> SELECT
    ->      sname,low_num
    -> FROM
    ->      student
    -> INNER JOIN ( SELECT student_id, num low_num FROM score WHERE course_id = 1 GROUP BY student_id HAVING num < 60 ) t1 ON student.sid = t1.student_id;
+--------+---------+
| sname  | low_num |
+--------+---------+
| 理解   |      10 |
| 钢蛋   |       8 |
| 张四   |       9 |
| 铁锤   |       9 |
| 李三   |       9 |
+--------+---------+
5 rows in set (0.00 sec)

#19、查询在所有选修了李平老师课程的学生中，这些课程(李平老师的课程，不是所有课程)平均成绩最高的学生姓名
mysql> SELECT
    ->     sname
    -> FROM
    ->     student
    -> WHERE
    ->     sid = (
    ->         SELECT
    ->             student_id
    ->         FROM
    ->             score
    ->         WHERE
    ->             course_id IN (
    ->                 SELECT
    ->                     course.cid
    ->                 FROM
    ->                     course
    ->                 INNER JOIN teacher ON course.teacher_id = teacher.tid
    ->                 WHERE
    ->                     teacher.tname = '李平老师'
    ->             )
    ->         GROUP BY
    ->             student_id
    ->         ORDER BY
    ->             AVG(num) DESC
    ->         LIMIT 1
    ->     );
+--------+
| sname  |
+--------+
| 张四   |
+--------+
1 row in set (0.00 sec)

# 20、查询每门课程成绩最好的前两名学生姓名
mysql> SELECT
    ->     *
    -> FROM
    ->     score
    -> ORDER BY
    ->     course_id,
    ->     num DESC;
+-----+------------+-----------+-----+
| sid | student_id | course_id | num |
+-----+------------+-----------+-----+
|  34 |          9 |         1 |  91 |
|  46 |         12 |         1 |  90 |
|  42 |         11 |         1 |  90 |
|  38 |         10 |         1 |  90 |
|  14 |          4 |         1 |  79 |
|  18 |          5 |         1 |  79 |
|  10 |          3 |         1 |  77 |
|   1 |          1 |         1 |  10 |
|  30 |          8 |         1 |   9 |
|  26 |          7 |         1 |   9 |
|  22 |          6 |         1 |   9 |
|   6 |          2 |         1 |   8 |
|  31 |          8 |         2 | 100 |
|  23 |          6 |         2 | 100 |
|  27 |          7 |         2 | 100 |
|  35 |          9 |         2 |  88 |
|  47 |         12 |         2 |  77 |
|  43 |         11 |         2 |  77 |
|  39 |         10 |         2 |  77 |
|  11 |          3 |         2 |  66 |
|  19 |          5 |         2 |  11 |
|  15 |          4 |         2 |  11 |
|   2 |          1 |         2 |   9 |
|  52 |         13 |         3 |  87 |
|  12 |          3 |         3 |  87 |
|   8 |          2 |         3 |  68 |
|  20 |          5 |         3 |  67 |
|  36 |          9 |         3 |  67 |
|  16 |          4 |         3 |  67 |
|  24 |          6 |         3 |  67 |
|  32 |          8 |         3 |  67 |
|  28 |          7 |         3 |  67 |
|  48 |         12 |         3 |  43 |
|  44 |         11 |         3 |  43 |
|  40 |         10 |         3 |  43 |
|  21 |          5 |         4 | 100 |
|  17 |          4 |         4 | 100 |
|  25 |          6 |         4 | 100 |
|   9 |          2 |         4 |  99 |
|  13 |          3 |         4 |  99 |
|  29 |          7 |         4 |  88 |
|  33 |          8 |         4 |  88 |
|  41 |         10 |         4 |  87 |
|  49 |         12 |         4 |  87 |
|  45 |         11 |         4 |  87 |
|   5 |          1 |         4 |  66 |
|  37 |          9 |         4 |  22 |
+-----+------------+-----------+-----+
47 rows in set (0.00 sec)