SELECT student_name,
       CASE 
           WHEN score >= 90 THEN 'A'
           WHEN score >= 80 THEN 'B'
           WHEN score >= 70 THEN 'C'
           ELSE 'F'
       END AS grade
FROM exam_results;
-- Output:
student_name    | grade
----------------|-------
John Smith      | A
Maria Garcia    | A
James Brown     | B
Sarah Wilson    | B
Michael Lee     | C
Emily Davis     | C
David Martinez  | F

SELECT order_id,
       CASE status
           WHEN 'P' THEN 'Pending'
           WHEN 'S' THEN 'Shipped'
           WHEN 'D' THEN 'Delivered'
           ELSE 'Unknown'
       END AS order_status
FROM orders;
-- Output:
order_id    | order_status
------------|-------------
1001        | Pending
1002        | Shipped
1003        | Delivered
1004        | Pending
1005        | Shipped
1006        | Unknown
1007        | Delivered

SELECT COUNT(*) as total_orders,
       SUM(CASE 
           WHEN status = 'Completed' THEN 1 
           ELSE 0 
       END) as completed_orders
FROM orders;
-- Output:
total_orders | completed_orders
-------------|------------------
1000         | 750