Is iOS IDFA and android advertising id unique to each other? I mean, can I store both values in the same column (advertising_id) and stay assured that it's not possible to have an iOS IDFA (from one device) that is also the same number of an Android Advertising ID (from another device)?
In iOS, both advertisingIdentifier and identifierForVendor are UUIDs. On the other hand, the Google Advertising ID is a text string with an unspecified format. While currently, this format appears to be a UUID as well, the documentation doesn't state what format Advertising IDs have; thus, you should assume this format may change in the future. (Be sure to review the information given in "Best practices for unique identifiers"; perhaps a different identifier than an "advertising ID" may serve your purposes better.)