add 1809

Author: fishercoder1534

Diff for: database/_1809.sql

@@ -0,0 +1,13 @@
+-- Write your PostgreSQL query statement below
+-- my completely original solution
+with sessions_with_ads as (select p.customer_id, p.session_id, p.start_time, p.end_time, a.timestamp as ts, a.ad_id
+                           from Playback p
+                                    inner join Ads a
+                                               on p.customer_id = a.customer_id and
+                                                  a.timestamp between p.start_time and p.end_time)
+
+select distinct(session_id)
+from (select distinct(session_id) from Playback)
+where session_id not in (select distinct(session_id) from sessions_with_ads)
+
+

Diff for: paginated_contents/database/README.md

@@ -8,6 +8,7 @@
 | 2072 |[The Winner University](https://leetcode.com/problems/the-winner-university/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_2072.sql)                                || Easy |
 | 2026 |[Low-Quality Problems](https://leetcode.com/problems/low-quality-problems/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_2026.sql)                                || Easy |
 | 1978 |[Employees Whose Manager Left the Company](https://leetcode.com/problems/employees-whose-manager-left-the-company/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_1978.sql)                                || Easy |
+| 1809 |[Ad-Free Sessions](https://leetcode.com/problems/ad-free-sessions/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_1809.sql)                                || Easy |
 | 1795 |[Rearrange Products Table](https://leetcode.com/problems/rearrange-products-table/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_1795.sql)                                || Easy |
 | 1789 |[Primary Department for Each Employee](https://leetcode.com/problems/primary-department-for-each-employee/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_1789.sql)                                || Easy |
 | 1757 |[Recyclable and Low Fat Products](https://leetcode.com/problems/recyclable-and-low-fat-products/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_1757.sql)                                || Easy |