# 1809. Ad-Free Sessions

<https://leetcode.com/problems/ad-free-sessions>

## Description

Table: `Playback`

```
+-------------+------+
| Column Name | Type |
+-------------+------+
| session\_id  | int  |
| customer\_id | int  |
| start\_time  | int  |
| end\_time    | int  |
+-------------+------+
session\_id is the primary key 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 |
+-------------+------+
| ad\_id       | int  |
| customer\_id | int  |
| timestamp   | int  |
+-------------+------+
ad\_id is the primary key for this table.
customer\_id is the ID of the customer viewing this ad.
timestamp is the moment of time at which the ad was shown.
```

Write an SQL query to report all the sessions that did not get shown any ads.

Return the result table in **any order**.

The query result format is in the following example:

```
Playback table:
+------------+-------------+------------+----------+
| session\_id | customer\_id | start\_time | end\_time |
+------------+-------------+------------+----------+
| 1          | 1           | 1          | 5        |
| 2          | 1           | 15         | 23       |
| 3          | 2           | 10         | 12       |
| 4          | 2           | 17         | 28       |
| 5          | 2           | 2          | 8        |
+------------+-------------+------------+----------+
Ads table:
+-------+-------------+-----------+
| ad\_id | customer\_id | timestamp |
+-------+-------------+-----------+
| 1     | 1           | 5         |
| 2     | 2           | 17        |
| 3     | 2           | 20        |
+-------+-------------+-----------+
Result table:
+------------+
| session\_id |
+------------+
| 2          |
| 3          |
| 5          |
+------------+
The ad with ID 1 was shown to user 1 at time 5 while they were in session 1.
The ad with ID 2 was shown to user 2 at time 17 while they were in session 4.
The ad with ID 3 was shown to user 2 at time 20 while they were in session 4.
We can see that sessions 1 and 4 had at least one ad. Sessions 2, 3, and 5 did not have any ads, so we return them.
```

## ac

```java
```