mysql> select * from course;
+----+-------------+
| id | course_name |
+----+-------------+
|  1 | Java        |
|  2 | MySQL       |
|  3 | Python      |
|  4 | Go          |
|  5 | C++         |
+----+-------------+
5 rows in set (0.00 sec)

mysql> select * from students;
+------+--------+------+------+--------+-----------+
| id   | name   | age  | sex  | height | course_id |
+------+--------+------+------+--------+-----------+
|    1 | Danny  |   25 |    1 |    160 |         1 |
|    2 | Green  |   23 |    1 |    158 |         2 |
|    3 | Henry  |   23 |    0 |    185 |         1 |
|    4 | Jane   |   22 |    1 |    162 |         3 |
|    5 | Jim    |   24 |    0 |    175 |         2 |
|    6 | John   |   21 |    0 |    172 |         4 |
|    7 | Lily   |   22 |    1 |    165 |         4 |
|    8 | Susan  |   23 |    1 |    170 |         5 |
|    9 | Thomas |   22 |    0 |    178 |         5 |
|   10 | Tom    |   23 |    0 |    165 |         5 |
+------+--------+------+------+--------+-----------+
10 rows in set (0.00 sec)

mysql> select * from stusex;
+------+------+
| id   | sex  |
+------+------+
|    0 | 女   |
|    1 | 男   |
+------+------+
2 rows in set (0.00 sec)

mysql> select s.id,s.name,s.age, d.sex,c.course_name from students s,stusex d,course c where s.sex = d.id and  s.course_id = c.id;
+------+--------+------+------+-------------+
| id   | name   | age  | sex  | course_name |
+------+--------+------+------+-------------+
|    1 | Danny  |   25 | 男   | Java        |
|    2 | Green  |   23 | 男   | MySQL       |
|    3 | Henry  |   23 | 女   | Java        |
|    4 | Jane   |   22 | 男   | Python      |
|    5 | Jim    |   24 | 女   | MySQL       |
|    6 | John   |   21 | 女   | Go          |
|    7 | Lily   |   22 | 男   | Go          |
|    8 | Susan  |   23 | 男   | C++         |
|    9 | Thomas |   22 | 女   | C++         |
|   10 | Tom    |   23 | 女   | C++         |
+------+--------+------+------+-------------+
10 rows in set (0.00 sec)