BigQuery SQL Event Attribution

Hello, thanks for reviewing. I am looking to have some SQL written that will run on BigQuery with standard SQL to attribute some actions to events that took place before the action following some rules. I will provide 3 tables of dummy data impressions, clicks & activities with the following schema:: activities: user_id STRING timestamp INTEGER activity_id STRING impressions & clicks: user_id STRING timestamp INTEGER campaign_id STRING site_id STRING The SQL should take all actions in the activity table and identify the last event in the impression/click table that occurred prior to the time of the action. It also needs to follow the rule of; if a click existed in the previous events leading up to the action, the click should get credit, if no click existed in the path leading up to the action, then the last impression prior to the action gets credit. The output should look something like: campaign_id | site_id | attributed_to_click | attributed_to_impression campaign_1 | site_1 | 2 | 1 campaign_1 | site_2 | 1 | 4 When the SQL is completed full comments should be added to explain the build. This may lead to more work on an on going basis.