You need these

SELECT * FROM gallery2 WHERE topic_id="1745987" UNION SELECT * FROM gallery2 WHERE topic_id="847985" UNION SELECT * FROM gallery2 WHERE topic_id="1513212" UNION SELECT * FROM gallery2 WHERE topic_id="345756" UNION SELECT * FROM gallery2 WHERE topic_id="389916" UNION SELECT * FROM gallery2 WHERE topic_id="1055683" UNION SELECT * FROM gallery2 WHERE topic_id="373655" UNION SELECT * FROM gallery2 WHERE topic_id="654240" UNION SELECT * FROM gallery2 WHERE topic_id="176349" UNION SELECT * FROM gallery2 WHERE topic_id="389208" UNION SELECT * FROM gallery2 WHERE topic_id="219070" UNION SELECT * FROM gallery2 WHERE topic_id="1246890" UNION SELECT * FROM gallery2 WHERE topic_id="1260932" UNION SELECT * FROM gallery2 WHERE topic_id="1508387" UNION SELECT * FROM gallery2 WHERE topic_id="303216" UNION SELECT * FROM gallery2 WHERE topic_id="919466"