SELECT
                 a.*,
                rem.nome AS remetente,
                des.nome AS destinatario,
                ure.nome AS ultimo_respondeu
           FROM
                ticket AS a

           INNER JOIN
                    usuarios rem ON rem.id = a.remetente_id
           LEFT JOIN
                    usuarios des ON des.id = a.destinatario_id
           LEFT JOIN
                    usuarios ure ON ure.id = a.ultimo_respondeu_id
           WHERE 1 = 1

     AND

     (SELECT COUNT(*)
          FROM
                usuarios AS b WHERE b.id = a.remetente_id
                     AND
                b.tipo = 1 ) >= 1