Sky Server DB Query 3-way join to find gravitational lens effect Table U: objd, color)11.8GB Table N: (objld, neighbored)41.8GB Find neighboring stars with similar colors Join u+n to find T=Ucolor, Nneighbored where U.objld=N. objld Join u+t to find U. objld where U. objld= T. neighborID and u color≈ TcolorSkyServer DB Query • 3-way join to find gravitational lens effect • Table U: (objId, color) 11.8GB • Table N: (objId, neighborId) 41.8GB • Find neighboring stars with similar colors: – Join U+N to find T = U.color,N.neighborId where U.objId = N.objId – Join U+T to find U.objId where U.objId = T.neighborID and U.color ≈ T.color