Retention is the number that tells you whether people actually like your product. The growth team wants to know: of the users active in January, how many came back in February? Using the user_activity table, find every user who was active in both January and February 2024. Return their user_id.
user_activity
| column | type |
|---|---|
| user_id | INTEGER |
| activity_date | DATE |
| user_id | activity_date |
|---|---|
| 1 | 2024-01-05 |
| 1 | 2024-01-20 |
| 1 | 2024-02-10 |
| 2 | 2024-01-15 |
| 3 | 2024-02-08 |
| 3 | 2024-02-22 |
| 4 | 2024-01-30 |
| 4 | 2024-02-14 |
| 5 | 2024-01-01 |
| user_id |
|---|
| 1 |
| 4 |
Users 1 and 4 have activity recorded in both January and February. User 2 and user 5 were only active in January; user 3 was only active in February.