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Asked: 2026-06-05T02:42:37+00:00

I have four tables like this: mysql> describe courses; +—————–+————-+——+—–+———+—————-+ | Field | Type

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I have four tables like this:

mysql> describe courses;
+-----------------+-------------+------+-----+---------+----------------+
| Field           | Type        | Null | Key | Default | Extra          |
+-----------------+-------------+------+-----+---------+----------------+
| course_id       | int(11)     | NO   | PRI | NULL    | auto_increment |
| course_name     | varchar(75) | YES  |     | NULL    |                |
| course_price_id | int(11)     | YES  | MUL | NULL    |                |
+-----------------+-------------+------+-----+---------+----------------+

mysql> describe pricegroups;
+-------------+--------------+------+-----+---------+----------------+
| Field       | Type         | Null | Key | Default | Extra          |
+-------------+--------------+------+-----+---------+----------------+
| price_id    | int(11)      | NO   | PRI | NULL    | auto_increment |
| price_name  | varchar(255) | YES  |     | NULL    |                |
| price_value | int(11)      | YES  |     | NULL    |                |
+-------------+--------------+------+-----+---------+----------------+

mysql> describe courseplans;
+------------+--------------+------+-----+---------+----------------+
| Field      | Type         | Null | Key | Default | Extra          |
+------------+--------------+------+-----+---------+----------------+
| plan_id    | int(11)      | NO   | PRI | NULL    | auto_increment |
| plan_name  | varchar(255) | YES  |     | NULL    |                |
| plan_time  | int(11)      | YES  |     | NULL    |                |
+------------+--------------+------+-----+---------+----------------+

mysql> describe course_to_plan;
+-----------+---------+------+-----+---------+-------+
| Field     | Type    | Null | Key | Default | Extra |
+-----------+---------+------+-----+---------+-------+
| course_id | int(11) | NO   | PRI | NULL    |       |
| plan_id   | int(11) | NO   | PRI | NULL    |       |
+-----------+---------+------+-----+---------+-------+

Let me try to explain what I have and what I would like to do…

All my courses (course_id) has different steps (plan_id) wich has a value of 1 or more days (plan_time).

A course has one or more steps (course_to_plan)

A course is connected to a pricegroup (price_id).

I would like to query my MySQL database and get an output off:
The course_name, the plan_id‘s it has, and based on the value of price_id together with the value in the plan_time get a result who looks something like this:

+------------+--------------+------------+---------+
| course_name| pricegroup   | plan_time  | RESULT  | 
+------------+--------------+------------+---------+
| Math       | Expensive    | 7          | 3500    |
+------------+--------------+------------+---------+

I hope you understand me…
Is it even possible with the structure I have or should I “rebuild-and-redo-correct” something?

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1 Answer

  1. Editorial Team
    SELECT c.course_name, p.price_name, SUM(cp.plan_time), SUM(cp.plan_time * p.price_value)
FROM courses c
    INNER JOIN pricegroups p        ON p.price_id = c.course_price_id
    INNER JOIN course_to_plan cpl   ON cpl.course_id = c.course_id
    INNER JOIN courseplans cp       ON cp.plan_id = cpl.plan_id
GROUP BY c.course_name, p.price_name

    Please note that it seems to me that your implementation might be erroneous. The way you want the data makes me think that you could be happier with a plan having a price, so you don’t apply the same price for a plan which is “expensive” AND another plan which is “cheap”, which is what you are doing at the moment. But I don’t really know, this is intuitive 🙂

    Thanks for accepting the answer, regards.

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