SELECT post.id
     FROM list_posts AS post
     LEFT OUTER JOIN private ON (post.id = private.pid AND private.uid = UIDGOESHERE)
     LEFT OUTER JOIN official_user AS adminu
     LEFT OUTER JOIN count_comments AS ccount ON (post.id = ccount.pid)
     WHERE
         post.id = PIDGOES HERE
        AND(
          post.private = false
         OR
          adminu.user = UIDGOESHERE
         OR
          count(private) = 1
        )
LIMIT 1