MySQL return value depending of date range - mysql

Question

I don't understand why my SQL query doesn't work. I'm trying to do that :
if date is null then return 0
if date < 15 min then return 1
if date > 15 min and < 30 min then return 2
if date > 30 min and < 60 min then return 3
if date > 60 min and < 180 min then return 4
if date > 180 min then return 5
So here is my SQL query :
SELECT CASE
WHEN start_date IS NULL THEN 0
WHEN start_date < DATE_SUB(NOW(),INTERVAL 15 MINUTE) THEN 1
WHEN start_date BETWEEN DATE_SUB(NOW(), INTERVAL 15 MINUTE) AND DATE_SUB(NOW(), INTERVAL 30 MINUTE) THEN 2
WHEN start_date BETWEEN DATE_SUB(NOW(), INTERVAL 30 MINUTE) AND DATE_SUB(NOW(), INTERVAL 60 MINUTE) THEN 3
WHEN start_date BETWEEN DATE_SUB(NOW(), INTERVAL 60 MINUTE) AND DATE_SUB(NOW(), INTERVAL 180 MINUTE) THEN 4
ELSE 5
END as remaining_time
FROM table
But I don't understand why when I got only the cases 0, 1 and 5. remaining_time is never in the. cases 2, 3 ,4.
Do you know why ?

Answer 1

Such condition will never be met, because the lower bound is greater than the higher bound:
start_date BETWEEN DATE_SUB(NOW(), INTERVAL 15 MINUTE) AND DATE_SUB(NOW(), INTERVAL 30 MINUTE)
You should have the bounds the other way around:
SELECT CASE
WHEN start_date IS NULL THEN 0
WHEN start_date < DATE_SUB(NOW(),INTERVAL 15 MINUTE) THEN 1
WHEN start_date BETWEEN DATE_SUB(NOW(), INTERVAL 30 MINUTE) AND DATE_SUB(NOW(), INTERVAL 15 MINUTE) THEN 2
WHEN start_date BETWEEN DATE_SUB(NOW(), INTERVAL 60 MINUTE) AND DATE_SUB(NOW(), INTERVAL 30 MINUTE) THEN 3
WHEN start_date BETWEEN DATE_SUB(NOW(), INTERVAL 180 MINUTE) AND DATE_SUB(NOW(), INTERVAL 60 MINUTE) THEN 4
ELSE 5
END as remaining_time
FROM table
CASE stops on the first matching condition, so this can be simplified as follows:
SELECT CASE
WHEN start_date is NULL THEN 0
WHEN start_date < NOW() - INTERVAL 15 MINUTE THEN 1
WHEN start_date < NOW() - INTERVAL 30 MINUTE THEN 2
WHEN start_date < NOW() - INTERVAL 60 MINUTE THEN 3
WHEN start_date < NOW() - INTERVAL 180 MINUTE THEN 4
ELSE 5
END as remaining_time
FROM table