Sum of multiplication of columns for rows with sim

Question

I have 3 columns in a table called "purchases":

id         amount         price
2          2              21
2          5              9
3          8              5

I want to group all rows with similar IDs and have this array as a result:

array([0] => [id => 2, total => 87 (because 2*21+5*9=87)], [1] => [id => 3, total => 40 (because 8*5=40)])

as total accounts for SUM(amount*price) for rows with similar IDs.

I've tried using

SELECT id, SUM(p.price*p.amount) total FROM purchases p GROUP by p.id

but it doesn't work well (i.e. it doesn't achieve what I want, which is what I wrote above). Any ideas on how to do this in mysql?

An example of what the query returns:

    id         amount         price
    2          3              89
    2          3              19

    SELECT id, SUM(p.price*p.amount) total FROM purchases p GROUP by p.id

==> [id => 2, total => 183]

Answer 1

@sombe: I've just tested your query and it works just fine. Are you sure your mysql is up to date?

The second works fine too:

Answer 2

SELECT
id, 
SUM(amount*price) AS total
FROM mytable
GROUP BY id

Data:

| id | amount | price |
|----|--------|-------|
| 2  | 3      | 19    |
| 2  | 3      | 89    |
| 3  | 203    | 1     |

Result:

id  total
2   324
3   203