Deleted Characters Being Reviewed

How would date_of_first_completed_quest be a join? Create_date, update_date - These are all columns in a database as would date_of_first_completed_quest be whether or not it exists, rationally. They are not referred to as joins by DBAs/coders. Where are you getting your information from?

Because there is no magic date_of_first_completed_quest column, that was a reference to a concept, not an entity.
It would be found by joining the Character table to earliest entry from the QuestComplete or QuestPerform table. Nexon doesn't even store the character level in the Character table, it's in it's own table, so why would you assume something as random and unnecessary as first_completed_quest would exist as a dedicated field in a table? Each active quest has it's own date/time field per character indicating when it was started and finished, to find the earliest you would specifically query the min() date of the appropriate table and join that result to the character table. Thank you ever so much for explaining to me the nomenclature of the job I've had for over a decade, truly.