Guardate il pelo.

SELECT * FROM gallery2 WHERE topic_id="1638924" UNION SELECT * FROM gallery2 WHERE topic_id="1352853" UNION SELECT * FROM gallery2 WHERE topic_id="863858" UNION SELECT * FROM gallery2 WHERE topic_id="1139899" UNION SELECT * FROM gallery2 WHERE topic_id="1013729" UNION SELECT * FROM gallery2 WHERE topic_id="1545139" UNION SELECT * FROM gallery2 WHERE topic_id="18331" UNION SELECT * FROM gallery2 WHERE topic_id="613288" UNION SELECT * FROM gallery2 WHERE topic_id="1531086" UNION SELECT * FROM gallery2 WHERE topic_id="340424" UNION SELECT * FROM gallery2 WHERE topic_id="378449" UNION SELECT * FROM gallery2 WHERE topic_id="1098123" UNION SELECT * FROM gallery2 WHERE topic_id="1378504" UNION SELECT * FROM gallery2 WHERE topic_id="994259" UNION SELECT * FROM gallery2 WHERE topic_id="344281" UNION SELECT * FROM gallery2 WHERE topic_id="941555"