Fixed cardinality estimation bug in CBO (#975)

Author: pavelvelikhov

ydb/library/yql/core/yql_cost_function.cpp

@@ -44,7 +44,7 @@ TOptimizerStatistics NYql::ComputeJoinStats(const TOptimizerStatistics& leftStat
     TVector<TString> joinedTableKeys;
 
     if (IsPKJoin(rightStats,rightJoinKeys)) {
-        newCard = std::max(leftStats.Nrows,rightStats.Nrows);
+        newCard = leftStats.Nrows;
         joinedTableKeys = leftStats.KeyColumns;
         if (leftStats.Type == EStatisticsType::BaseTable){
             outputType = EStatisticsType::FilteredFactTable;
@@ -53,7 +53,7 @@ TOptimizerStatistics NYql::ComputeJoinStats(const TOptimizerStatistics& leftStat
         }
     }
     else if (IsPKJoin(leftStats,leftJoinKeys)) {
-        newCard = std::max(leftStats.Nrows,rightStats.Nrows);
+        newCard = rightStats.Nrows;
         joinedTableKeys = rightStats.KeyColumns;
         if (rightStats.Type == EStatisticsType::BaseTable){
             outputType = EStatisticsType::FilteredFactTable;

ydb/library/yql/dq/opt/dq_opt_predicate_selectivity.cpp

@@ -96,7 +96,7 @@ double NYql::NDq::ComputePredicateSelectivity(const TExprBase& input, const std:
                     }
                 } else {
                     if (stats->Nrows > 1) {
-                        result = stats->Nrows / 10;
+                        result = 0.1;
                     }
                     else {
                         result = 1.0;