minor update to queries.sql

lab-3/music-store-app/sql/queries.sql

@@ -70,7 +70,7 @@ DELETE FROM Track WHERE album_upc='726517237627'; /* EXAMPLE */
 
 /* ------------------------------------ */
 
-/* 5. Retrieve details about an order
+/* 5a. Retrieve details about an order
 Include the customer_id, delivery method
 and total order value in the result-set */
 
@@ -81,3 +81,20 @@ INNER JOIN LineItem
 INNER JOIN Album 
 	ON Album.upc=LineItem.album_upc
 WHERE Transaction.id=1; /* EXAMPLE */
+
+/* 5b. Retrieve details about an order
+Include the transaction id, customer_id
+and the number of items ordered in the 
+result-set */
+SELECT t.id, t.customer_id, SUM(li.quantity) AS num_items 
+FROM Transaction t 
+INNER JOIN LineItem li 
+	ON t.id=li.trans_id 
+GROUP BY t.id; /* group results by transaction id */
+
+/* 5c. Does the same as the previous query
+but using a nested query rather than a JOIN */
+SELECT t.id, t.customer_id, 
+(SELECT SUM(li.quantity) FROM LineItem li 
+	WHERE li.trans_id=t.id) AS num_items
+FROM Transaction t;