MySQL join four tables and get some kind of SUM result - mysql

Question

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?

Answer 1

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.

Answer 2

Let me see if I understand what you need:
SELECT c.course_name, pg.price_name,
COUNT(cp.plan_time), SUM(pg.price_value * cp.plan_time) AS result
FROM courses c
INNER JOIN pricegroups pg ON c.course_price_id = pg.price_id
INNER JOIN course_to_plan ctp ON c.course_id = ctp.course_id
INNER JOIN courseplans cp ON ctp.plan_id = cp.plan_id
GROUP BY c.couse_name, pg.price_name