dec memory cost

src/main/scala/com/aliyun/odps/spark/examples/makedata_recsys/video_dssm_sampler.scala

@@ -158,8 +158,6 @@ object video_dssm_sampler {
           floor((col("pos_id") - 1) / 100) === col("group_id"))
         .where(col("vid") =!= col("vid_left") && col("vid") =!= col("vid_right"))
         .select(
-          col("dt"),
-          col("hh"),
           lit(null).as("extend"),
           lit(null).as("view_24h"),
           lit(null).as("total_return_uv"),