Grokking SQL for Tech Interviews
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19. Ad-Free Sessions

Problem

Table: Playback

+-------------+------+
| Column Name | Type |
+-------------+------+
| session_id  | int  |
| customer_id | int  |
| start_time  | int  |
| end_time    | int  |
+-------------+------+
session_id is the column with unique values for this table.
customer_id is the ID of the customer watching this session.
The session runs during the inclusive interval between start_time and end_time.
It is guaranteed that start_time <= end_time and that two sessions for the same customer do not intersect.

Table: Ads

+-------------+------+
| Column Name | Type |

.....

.....

.....

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Christopher Guy Slater

Christopher Guy Slater

· 6 days ago

SELECT 
  session_id
FROM Playback p
WHERE NOT EXISTS(
  SELECT 1
  FROM Ads a  
    WHERE p.customer_id = a.customer_id
    AND a.timestamp BETWEEN p.start_time AND p.end_time
);

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