 #85 provide union query
 #85 provide union query

daewon/incubator-s2graph,SteamShon/incubator-s2graph,jongwook/incubator-s2graph,daewon/incubator-s2graph,jongwook/incubator-s2graph,SteamShon/incubator-s2graph,SteamShon/incubator-s2graph