feat: solved 3rd stage of the Hyperskill project "Electronics Store Customer"

Author: sswietoniowski

hyperskill/16_electronics_store_customer/02/README.md

@@ -6,7 +6,6 @@ Round the result up to 2 decimal places.
 
 ```sql
 SELECT ROUND(AVG(price), 2) AS avg_price
-  FROM Printer
- WHERE color = 'C'
-   AND type = 'Inkjet';
+FROM Printer
+WHERE color = 'C' AND type = 'Inkjet';
 ```

hyperskill/16_electronics_store_customer/03/README.md

@@ -0,0 +1,14 @@
+# Objectives
+
+Identify the total price of all laptop models produced by each maker.
+
+Find the maker in the `Product` table and `SUM` of the prices in Laptop as `total_price`.
+
+Ensure the results are sorted by `total_price` in ascending order. Use `GROUP_BY` and `SUM` functions to solve this.
+
+```sql
+SELECT maker, SUM(price) AS total_price
+FROM Product JOIN Laptop ON Product.model = Laptop.model
+GROUP BY maker
+ORDER BY total_price ASC;
+```