mysql> SELECT CategoryID, SUM(UnitsInStock) AS 'Calkowita liczba produktow w magazynie'
    -> FROM products
    -> GROUP BY CategoryID;
+------------+----------------------------------------+
| CategoryID | Calkowita liczba produktow w magazynie |
+------------+----------------------------------------+
|       NULL |                                      0 | 
|          1 |                                    559 | 
|          2 |                                    507 | 
|          3 |                                    386 | 
|          4 |                                    393 | 
|          5 |                                    308 | 
|          6 |                                    165 | 
|          7 |                                    100 | 
|          8 |                                    701 | 
+------------+----------------------------------------+
9 rows in set (0.34 sec)
