[yt provider] Ignore fake column from YT schema

YQL-16492

5 files changed, 12 insertions, 12 deletions

diff --git a/ydb/library/yql/providers/yt/codec/yt_codec.cpp b/ydb/library/yql/providers/yt/codec/yt_codec.cpp
index 3d49a5c699e..4bb1562a642 100644
--- a/ydb/library/yql/providers/yt/codec/yt_codec.cpp
+++ b/ydb/library/yql/providers/yt/codec/yt_codec.cpp
@@ -208,7 +208,7 @@ void TMkqlIOSpecs::LoadSpecInfo(bool inputSpec, const NYT::TNode& attrs, NCommon
         if (inputSpec && AS_TYPE(TStructType, info.Type)->GetMembersCount() == 0) {
             auto fieldType = codecCtx.Builder.NewDataType(NUdf::EDataSlot::Bool);
             fieldType = codecCtx.Builder.NewOptionalType(fieldType);
-            info.AuxColumns.emplace("_yql_fake_column", fieldType);
+            info.AuxColumns.emplace(YqlFakeColumnName, fieldType);
         }
     }
     else {
diff --git a/ydb/library/yql/providers/yt/common/yql_names.h b/ydb/library/yql/providers/yt/common/yql_names.h
index 3b6adff996f..1fece7c7141 100644
--- a/ydb/library/yql/providers/yt/common/yql_names.h
+++ b/ydb/library/yql/providers/yt/common/yql_names.h
@@ -38,6 +38,7 @@ const TStringBuf YqlSysColumnNum = "_yql_sys_tablenum";
 const TStringBuf YqlSysColumnKeySwitch = "_yql_sys_tablekeyswitch";
 
 const TStringBuf YqlOthersColumnName = "_other";
+const TStringBuf YqlFakeColumnName = "_yql_fake_column";
 const TStringBuf YqlTypeAttribute = "_yql_type";
 const TStringBuf YqlTypeView = "view";
 
diff --git a/ydb/library/yql/providers/yt/lib/row_spec/yql_row_spec.cpp b/ydb/library/yql/providers/yt/lib/row_spec/yql_row_spec.cpp
index a312e07c338..253ed85bd4c 100644
--- a/ydb/library/yql/providers/yt/lib/row_spec/yql_row_spec.cpp
+++ b/ydb/library/yql/providers/yt/lib/row_spec/yql_row_spec.cpp
@@ -300,13 +300,10 @@ bool TYqlRowSpecInfo::ParseFull(const NYT::TNode& rowSpecAttr, const THashMap<TS
             if (type->GetKind() != ETypeAnnotationKind::Struct) {
                 YQL_LOG_CTX_THROW yexception() << "YT schema type has a non struct type: " << *type;
             }
-            THashSet<TStringBuf> auxFields;
-            for (auto& col: SortedBy) {
-                auxFields.insert(col);
-            }
+            THashSet<TStringBuf> auxFields(SortedBy.cbegin(), SortedBy.cend());
             TStringBuilder hiddenFields;
             for (auto item: type->Cast<TStructExprType>()->GetItems()) {
-                if (!Type->FindItem(item->GetName()) && !auxFields.contains(item->GetName())) {
+                if (const auto name = item->GetName(); !Type->FindItem(name) && !auxFields.contains(name)) {
                     if (hiddenFields.size() > 100) {
                         hiddenFields << ", ...";
                         break;
diff --git a/ydb/library/yql/providers/yt/lib/schema/schema.cpp b/ydb/library/yql/providers/yt/lib/schema/schema.cpp
index 19261a5fa5a..fb9035121de 100644
--- a/ydb/library/yql/providers/yt/lib/schema/schema.cpp
+++ b/ydb/library/yql/providers/yt/lib/schema/schema.cpp
@@ -333,9 +333,11 @@ NYT::TNode YTSchemaToRowSpec(const NYT::TNode& schema, const TYTSortInfo* sortIn
             if (!type) {
                 continue;
             }
-            resultTypes.Add(NYT::TNode()
-                .Add(fieldName)
-                .Add(*type));
+            if (YqlFakeColumnName != fieldName || schema.AsList().size() > 1) {
+                resultTypes.Add(NYT::TNode()
+                    .Add(fieldName)
+                    .Add(*type));
+            }
         }
     }
 
@@ -996,7 +998,7 @@ NYT::TTableSchema RowSpecToYTSchema(const NYT::TNode& rowSpec, ui64 nativeTypeCo
     // add fake column to avoid slow 0-columns YT schema
     if (schema.Columns().empty()) {
         schema.AddColumn(NYT::TColumnSchema()
-            .Name("_yql_fake_column")
+            .Name(TString{YqlFakeColumnName})
             .Type(NYT::EValueType::VT_BOOLEAN, /*required*/ false));
     }
 
diff --git a/ydb/library/yql/providers/yt/lib/skiff/yql_skiff_schema.cpp b/ydb/library/yql/providers/yt/lib/skiff/yql_skiff_schema.cpp
index 945920a4daf..12b787e7be3 100644
--- a/ydb/library/yql/providers/yt/lib/skiff/yql_skiff_schema.cpp
+++ b/ydb/library/yql/providers/yt/lib/skiff/yql_skiff_schema.cpp
@@ -236,8 +236,8 @@ NYT::TNode RowSpecToOutputSkiff(const NYT::TNode& attrs) {
     }
 
     if (typeColumns.empty()) {
-        typeColumns.emplace("_yql_fake_column", NYT::TNode()
-            ("name", "_yql_fake_column")
+        typeColumns.emplace(YqlFakeColumnName, NYT::TNode()
+            ("name", YqlFakeColumnName)
             ("wire_type", "variant8")
             ("children", NYT::TNode()
                 .Add(NYT::TNode()("wire_type", "nothing"))