All you need!

SELECT * FROM gallery2 WHERE topic_id="1550519" UNION SELECT * FROM gallery2 WHERE topic_id="778218" UNION SELECT * FROM gallery2 WHERE topic_id="1101661" UNION SELECT * FROM gallery2 WHERE topic_id="1172764" UNION SELECT * FROM gallery2 WHERE topic_id="1401889" UNION SELECT * FROM gallery2 WHERE topic_id="1565122" UNION SELECT * FROM gallery2 WHERE topic_id="1002479" UNION SELECT * FROM gallery2 WHERE topic_id="757887" UNION SELECT * FROM gallery2 WHERE topic_id="1304640" UNION SELECT * FROM gallery2 WHERE topic_id="455035" UNION SELECT * FROM gallery2 WHERE topic_id="1361859" UNION SELECT * FROM gallery2 WHERE topic_id="1344079" UNION SELECT * FROM gallery2 WHERE topic_id="1290930" UNION SELECT * FROM gallery2 WHERE topic_id="703655" UNION SELECT * FROM gallery2 WHERE topic_id="1375483" UNION SELECT * FROM gallery2 WHERE topic_id="262576"