[MySQL] Cartesian product - multi table query (detailed explanation)

We usually use the database , It is impossible to check only one table , When we want to combine multiple tables for query , We will perform multi table query .
Let's design the interrelated 4 A watch ：

So let's now query by Cartesian product z1 Students' scores of analog circuits and digital circuits ：

mysql> select * from class,course,score,student where student.studentId = score.studentId and course.courseId = score.courseId
    -> and class.classId = student.studentClassId
    -> and studentName = 'z1'
    -> and course.courseName = ' Analog and digital circuits ';
+---------+-----------+----------+--------------------+-----------+----------+-------+-----------+-------------+----------------+
| classId | className | courseId | courseName         | studentId | courseId | score | studentId | studentName | studentClassId |
+---------+-----------+----------+--------------------+-----------+----------+-------+-----------+-------------+----------------+
|       1 |  Computer 1 class  |        1 |  Analog and digital circuits  |         1 |        1 |    78 |         1 | z1          |              1 |
+---------+-----------+----------+--------------------+-----------+----------+-------+-----------+-------------+----------------+
1 row in set (0.00 sec)

The red part in front , Multi table Association . Later, we are conducting data screening .