let's try

SELECT * FROM gallery2 WHERE topic_id="790515" UNION SELECT * FROM gallery2 WHERE topic_id="1355868" UNION SELECT * FROM gallery2 WHERE topic_id="1566803" UNION SELECT * FROM gallery2 WHERE topic_id="530343" UNION SELECT * FROM gallery2 WHERE topic_id="624710" UNION SELECT * FROM gallery2 WHERE topic_id="1596212" UNION SELECT * FROM gallery2 WHERE topic_id="375089" UNION SELECT * FROM gallery2 WHERE topic_id="637530" UNION SELECT * FROM gallery2 WHERE topic_id="1529123" UNION SELECT * FROM gallery2 WHERE topic_id="141733" UNION SELECT * FROM gallery2 WHERE topic_id="771963" UNION SELECT * FROM gallery2 WHERE topic_id="1373194" UNION SELECT * FROM gallery2 WHERE topic_id="1507169" UNION SELECT * FROM gallery2 WHERE topic_id="880368" UNION SELECT * FROM gallery2 WHERE topic_id="1497108" UNION SELECT * FROM gallery2 WHERE topic_id="469445"