It is and it was (is?) for a long the time mandatory join style for UPDATE statement. Reason being that it's used to declare and restrict which table should be

It is and it was (is?) for a long the time mandatory join style for UPDATE statement. Reason being that it's used to declare and restrict which table should be updated in the UPDATE section as opposed to optional joined tables listed in the FROM section. PS: The *= is plateform specific however (have no clue which). Usually you just write a more SQL standard WHERE section.