Mention the username of Facebook of Ralph Abraham.
username of Facebook refers to facebook; Ralph Abraham is an official_full_name; official_full_name refers to first_name, last_name
SELECT T2.facebook FROM current AS T1 INNER JOIN `social-media` AS T2 ON T2.bioguide = T1.bioguide_id WHERE T1.first_name = 'Ralph' AND T1.last_name = 'Abraham'