How many official social media does Mark Warner have?
official social media refers to facebook is not null, instagram is not null, twitter is not null, youtube is not null; Mark Warner is an official_full_name; official_full_name refers to first_name, last_name
SELECT CASE WHEN T1.facebook IS NOT NULL THEN 1 END + CASE WHEN T1.instagram IS NOT NULL THEN 1 END + CASE WHEN T1.twitter IS NOT NULL THEN 1 END + CASE WHEN T1.youtube IS NOT NULL THEN 1 END AS COUNTSOCIAL FROM `social-media` AS T1 INNER JOIN current AS T2 ON T1.bioguide = T2.bioguide_id WHERE T2.first_name = 'Mark' AND T2.last_name = 'Warner'