| 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 |

| ad_id | customer_id | timestamp | | ----- | ----------- | --------- | | 1 | 1 | 5 | | 2 | 2 | 17 | | 3 | 2 | 20 |