INSERT INTO userattributes ( userID, . . . )
SELECT u.userID, . . .
FROM users u
WHERE NOT EXISTS (SELECT * FROM userattributes a WHERE a.userID = u.userID)
INSERT INTO table2 (file_index, celeb_name) SELECT file_index, 'userID' FROM table1 WHERE filename = 'user' AND file_index NOT IN (SELECT DISTINCT file_index FROM table2 WHERE user_name = 'userID')