address comments

executor/builder.go

@@ -581,30 +581,24 @@ func (b *executorBuilder) buildHashJoin(v *plan.PhysicalHashJoin) Executor {
 	}
 
 	defaultValues := v.DefaultValues
+	if defaultValues == nil {
+		defaultValues = make([]types.Datum, e.innerExec.Schema().Len())
+	}
+	e.resultGenerator = newJoinResultGenerator(b.ctx, v.JoinType, v.SmallChildIdx == 0, defaultValues, v.OtherConditions, nil, nil)
 	if v.SmallChildIdx == 0 {
 		e.innerExec = leftExec
 		e.outerExec = rightExec
 		e.innerFilter = v.LeftConditions
 		e.outerFilter = v.RightConditions
 		e.innerKeys = leftHashKey
 		e.outerKeys = rightHashKey
-		if defaultValues == nil {
-			defaultValues = make([]types.Datum, e.innerExec.Schema().Len())
-		}
-		e.resultGenerator = newJoinResultGenerator(b.ctx, v.JoinType, v.SmallChildIdx == 0, defaultValues,
-			v.OtherConditions, nil, nil)
 	} else {
 		e.innerExec = rightExec
 		e.outerExec = leftExec
 		e.innerFilter = v.RightConditions
 		e.outerFilter = v.LeftConditions
 		e.innerKeys = rightHashKey
 		e.outerKeys = leftHashKey
-		if defaultValues == nil {
-			defaultValues = make([]types.Datum, e.innerExec.Schema().Len())
-		}
-		e.resultGenerator = newJoinResultGenerator(b.ctx, v.JoinType, v.SmallChildIdx == 0, defaultValues,
-			v.OtherConditions, nil, nil)
 	}
 
 	return e

plan/logical_plans.go

@@ -106,9 +106,10 @@ type LogicalJoin struct {
 	leftProperties  [][]*expression.Column
 	rightProperties [][]*expression.Column
 
-	// DefaultValues is only used for outer join, which is values the inner table's  should be when the outer table
-	// doesn't match any inner table'row.
+	// DefaultValues is only used for left/right outer join, which is values the inner row's should be when the outer table
+	// doesn't match any inner table's row.
 	// That it's nil just means the default values is a slice of NULL.
+	// Currently, only `aggregation push down` phase will set this.
 	DefaultValues []types.Datum
 
 	// redundantSchema contains columns which are eliminated in join.