MySQL - What's the total cost in price for each person's total number of courses?

Question

I am having problems working out a sum in a query. It requires a CAST I'm sure.

The query - I want to find out how much each parents total number of activities costs. The price of each activity is $5.50, therefore someone with 4 activities would be $22 total.

It requires 3 columns which are for Parent Name, total activities, and total cost.

I can't work out the total cost for each parent's total activities...

Please help

code

SELECT CONCAT_WS(" ", P.parent_title, P.parent_fname, P.parent_sname) AS Parent,
COUNT(A.activity_name) AS Total_Activities
FROM Activity A, Child C, Parent P, ChildActivity
WHERE P.parent_id = C.parent_id
AND C.child_id = ChildActivity.child_id
AND A.activity_id = ChildActivity.activity_id
GROUP BY Parent
ORDER BY P.parent_sname, P.parent_fname

Results example: (actually lists 11 people)

  *Parent*        *Total Activities*
  MR James Dean         4

Answer 1

As this is homework, I can not give you the answer right away. Think it this way: You can apply math to column values :)