SELECT DISTINCT a.id_cat, a.on_main, a.name_cat, a.comment_cat, a.link_cat, a.dt_begin
FROM catalog AS a
LEFT JOIN category_relation AS b
ON (a.id_cat=b.id_obj)
WHERE a.type_cat='object_halls_testing'
AND a.visibility_cat = '1'
#AND a.dt_begin < '2019-12-10 16'
#AND a.dt_end > '2019-12-10 16'
AND a.rn_id=45
ORDER BY a.dt_begin DESC
LIMIT 300