Q99.Marks: +2.0UGC NET Paper 2: Computer Science 18th June 2024 Shift 1 (Cancelled)
📄 Passage
Answer the following 5 questions based on the passage.
A company is implementing a new database system to manage its customer information. The database contains tables for customers, orders, products and sales representatives. Each customer can place multiple orders and each order can contain multiple products. Each order is associated with a specific sales representatives who manages the account. The database is designed to improve efficiency in tracking sales and customer interactions.
Which SQL query retrieves the total number of orders placed by a specific customer ?
1.Select COUNT (*) As total_orders from orders where customer_id = [Customer_ID];
2.Select COUNT (order_id) As total_orders from orders where customer_id = [Customer_ID];✓ Correct
3.Select COUNT (DISTINCT order_id) As total_orders from orders Where customer_id = [ Customer_ID];
4.Select SUM (order_Id) As total_orders from orders where customer_id = [Customer_ID];
Solution
The correct answer is Option 2: Select COUNT (order_id) As total_orders from orders where customer_id = [Customer_ID];.
Key Points
The query Select COUNT (order_id) As total_orders from orders where customer_id = [Customer_ID]; accurately counts the total number of orders placed by a specific customer identified by [Customer_ID].
The COUNT(order_id) function counts the number of rows where order_id is not null, effectively giving the total number of orders for that customer.
Additional Information
Option 1: Select COUNT (*) As total_orders from orders where customer_id = [Customer_ID]; also counts the total number of orders but includes all rows regardless of whether order_id is null or not. Generally, order_id is not null, so this option might still give the correct count but is less specific.
Option 3: Select COUNT (DISTINCT order_id) As total_orders from orders Where customer_id = [ Customer_ID]; counts the number of distinct order_id, which would be correct if there are no duplicate order_ids for a single customer. This option is more specific but redundant if order_ids are unique by default.
Option 4: Select SUM (order_Id) As total_orders from orders where customer_id = [Customer_ID]; is incorrect because it sums the values of order_id rather than counting them, which does not provide the number of orders.
