Sum of multiplication of columns for rows with similar IDs in MySQL

Question

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

id         amount         price
2          2              21
2          5              9
3          8               


        

Answer 1

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