| auction_id | 1 | Unique ID for every bid request in the system. A joining key for all the events associated with the bid request, like impression, clicks, and activities. | VARCHAR(255) | |
| user_id | 2 | Device ID for mobile, cookie for desktop. Will populate with cookie on a desktop OR an iOS/Android ID for mobile | VARCHAR(255) | |
| user_id_hashed | 3 | GDPR-compliant hashed user_id | VARCHAR(255) | |
| segment_id | 4 | AIDEM segment ID; contains all segments the user qualifies for, comma-delimited, regardless if it is targeted on the line item that won | N/A | The length of this field is unbounded since there can be many segment IDs that a user qualifies for |
