SQL -problem -subscription

Source:https://www.interviewquery.com/questions/subscription-overlap

Given a table of product subscriptions with a subscription start date and end date for each user, write a query that returns true or false whether or not each user has a subscription date range that overlaps with any other completed subscription.

Completed subscriptions have end_date recorded.

Example:

Input:

subscriptions table

Column	Type
user_id	INTEGER
start_date	DATETIME
end_date	DATETIME

user_id	start_date	end_date
1	2019-01-01	2019-01-31
2	2019-01-15	2019-01-17
3	2019-01-29	2019-02-04
4	2019-02-05	2019-02-10

Output:

user_id	overlap
1	1
2	1
3	1
4	0

WITH over_lap AS (
    SELECT s2.start_date, s2.end_date, s2.user_id, 1 AS is_overlap
    FROM subscriptions s1
    JOIN subscriptions s2 ON s1.user_id != s2.user_id
    AND (
        s2.start_date BETWEEN s1.start_date AND s1.end_date
        OR s2.end_date BETWEEN s1.start_date AND s1.end_date
    )
)
-- Get users with overlaps
SELECT c.user_id, c.is_overlap
FROM over_lap c

UNION ALL

-- Get users without overlaps
SELECT s3.user_id, 0 AS is_overlap
FROM subscriptions s3
WHERE NOT EXISTS (
    SELECT 1 
    FROM over_lap ol 
    WHERE ol.user_id = s3.user_id
);