[GitHub] incubator-quickstep pull request #332: Small adjustments in star schema cost...

[zuyu]

Github user zuyu commented on a diff in the pull request:

    https://github.com/apache/incubator-quickstep/pull/332#discussion_r167114902
  
    --- Diff: query_optimizer/cost_model/StarSchemaSimpleCostModel.cpp ---
    @@ -493,7 +493,7 @@ std::size_t 
StarSchemaSimpleCostModel::getNumDistinctValues(
           return stat.getNumDistinctValues(rel_attr_id);
         }
       }
    -  return estimateCardinalityForTableReference(table_reference);
    +  return estimateCardinalityForTableReference(table_reference) * 0.1;
    --- End diff --
    
    Could you please explain more regarding why `0.1` would be a good guess for 
the number of distinct values?


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