Classify ride pickups by waiting time

The rider-experience team wants a quick service-level view of how long customers waited for a driver to arrive.

From ride_requests, return ride_id, rider_name, wait_minutes and a new column wait_band:

• Not picked up when wait_minutes is NULL (the ride was cancelled before a driver arrived)
• Quick for 3 minutes or less
• Normal for 4 to 8 minutes
• Slow for anything above 8 minutes

Order the result by ride_id.

1. Step 1: `CASE` evaluates branches top to bottom and stops at the first match, so ordering matters.
2. Step 2: Test `IS NULL` first. A NULL compared with `<= 3` is unknown, so it would silently fall through to `ELSE 'Slow'`.
3. Step 3: Because earlier branches already caught the smaller values, `<= 8` only needs one boundary to describe 4 to 8.

SELECT ride_id,
       rider_name,
       wait_minutes,
       CASE
         WHEN wait_minutes IS NULL THEN 'Not picked up'
         WHEN wait_minutes <= 3    THEN 'Quick'
         WHEN wait_minutes <= 8    THEN 'Normal'
         ELSE 'Slow'
       END AS wait_band
FROM ride_requests
ORDER BY ride_id;