impl

src/Storages/ColumnsDescription.cpp

@@ -851,7 +851,6 @@ std::optional<ColumnDefault> ColumnsDescription::getDefault(const String & colum
     return {};
 }
 
-
 bool ColumnsDescription::hasCompressionCodec(const String & column_name) const
 {
     const auto it = columns.get<1>().find(column_name);

src/Storages/MergeTree/ExportPartTask.cpp

@@ -4,17 +4,20 @@
 #include <Storages/MergeTree/MergeTreeData.h>
 #include <Interpreters/Context.h>
 #include <Interpreters/DatabaseCatalog.h>
+#include <Interpreters/inplaceBlockConversions.h>
 #include <Core/Settings.h>
 #include <Interpreters/ExpressionActions.h>
 #include <Processors/Executors/CompletedPipelineExecutor.h>
 #include <Processors/QueryPlan/BuildQueryPipelineSettings.h>
 #include <Processors/QueryPlan/Optimizations/QueryPlanOptimizationSettings.h>
 #include <Processors/QueryPlan/QueryPlan.h>
+#include <Processors/QueryPlan/ExpressionStep.h>
 #include <QueryPipeline/QueryPipelineBuilder.h>
 #include <Common/Exception.h>
 #include <Common/ProfileEventsScope.h>
 #include <Storages/MergeTree/ExportList.h>
 #include <Formats/FormatFactory.h>
+#include <Databases/enableAllExperimentalSettings.h>
 
 namespace ProfileEvents
 {
@@ -58,7 +61,11 @@ bool ExportPartTask::executeStep()
 
     const auto & metadata_snapshot = manifest.metadata_snapshot;
 
+    // Read only physical columns from the part
     Names columns_to_read = metadata_snapshot->getColumns().getNamesOfPhysical();
+
+    // But we want all columns (including aliases) in the output
+    NamesAndTypesList all_columns = metadata_snapshot->getColumns().getAll();
 
     MergeTreeSequentialSourceType read_type = MergeTreeSequentialSourceType::Export;
 
@@ -146,6 +153,34 @@ bool ExportPartTask::executeStep()
             local_context,
             getLogger("ExportPartition"));
 
+        // Add expression step to compute alias and other default columns for export
+        // This materializes virtual columns (like ALIAS) so they can be written to output
+        const auto & current_header = plan_for_part.getCurrentHeader();
+
+        // Enable all experimental settings for default expressions
+        // (same pattern as in IMergeTreeReader::evaluateMissingDefaults)
+        auto context_for_defaults = Context::createCopy(local_context);
+        enableAllExperimentalSettings(context_for_defaults);
+
+        auto defaults_dag = evaluateMissingDefaults(
+            *current_header,
+            all_columns,
+            metadata_snapshot->getColumns(),
+            context_for_defaults);
+
+        if (defaults_dag)
+        {
+            // Ensure columns are in the correct order matching all_columns
+            defaults_dag->removeUnusedActions(all_columns.getNames(), false);
+            defaults_dag->addMaterializingOutputActions(/*materialize_sparse=*/ false);
+
+            auto expression_step = std::make_unique<ExpressionStep>(
+                current_header,
+                std::move(*defaults_dag));
+            expression_step->setStepDescription("Compute alias and default expressions for export");
+            plan_for_part.addStep(std::move(expression_step));
+        }
+
         ThreadGroupSwitcher switcher((*exports_list_entry)->thread_group, "");
 
         QueryPlanOptimizationSettings optimization_settings(local_context);

src/Storages/MergeTree/MergeTreeData.cpp

@@ -6242,7 +6242,11 @@ void MergeTreeData::exportPartToTable(
     auto source_metadata_ptr = getInMemoryMetadataPtr();
     auto destination_metadata_ptr = dest_storage->getInMemoryMetadataPtr();
 
-    if (destination_metadata_ptr->getColumns().getAllPhysical().sizeOfDifference(source_metadata_ptr->getColumns().getAllPhysical()))
+    const auto & source_columns = source_metadata_ptr->getColumns();
+
+    const auto & destination_columns = destination_metadata_ptr->getColumns();
+
+    if (destination_columns.getAll().sizeOfDifference(source_columns.getAll()))
         throw Exception(ErrorCodes::INCOMPATIBLE_COLUMNS, "Tables have different structure");
 
     if (query_to_string(source_metadata_ptr->getPartitionKeyAST()) != query_to_string(destination_metadata_ptr->getPartitionKeyAST()))

tests/queries/0_stateless/03572_export_merge_tree_part_to_object_storage.reference

@@ -42,3 +42,17 @@
 ---- Count rows in big_table and big_destination_max_rows
 4194304
 4194304
+---- Test ALIAS columns export
+---- Verify ALIAS column data in source table (arr_1 computed from arr[1])
+1	[1,2,3]	1
+1	[10,20,30]	10
+---- Verify ALIAS column data exported to S3 (should match source)
+1	[1,2,3]	1
+1	[10,20,30]	10
+---- Test MATERIALIZED columns export
+---- Verify MATERIALIZED column data in source table (arr_1 computed from arr[1])
+1	[1,2,3]	1
+1	[10,20,30]	10
+---- Verify MATERIALIZED column data exported to S3 (should match source)
+1	[1,2,3]	1
+1	[10,20,30]	10

tests/queries/0_stateless/03572_export_merge_tree_part_to_object_storage.sh

@@ -18,12 +18,17 @@ mt_table_roundtrip="mt_table_roundtrip_${RANDOM}"
 big_table="big_table_${RANDOM}"
 big_destination_max_bytes="big_destination_max_bytes_${RANDOM}"
 big_destination_max_rows="big_destination_max_rows_${RANDOM}"
+mt_table_tf="mt_table_tf_${RANDOM}"
+mt_alias="mt_alias_${RANDOM}"
+mt_materialized="mt_materialized_${RANDOM}"
+s3_alias_export="s3_alias_export_${RANDOM}"
+s3_materialized_export="s3_materialized_export_${RANDOM}"
 
 query() {
     $CLICKHOUSE_CLIENT --query "$1"
 }
 
-query "DROP TABLE IF EXISTS $mt_table, $s3_table, $mt_table_roundtrip, $s3_table_wildcard, $s3_table_wildcard_partition_expression_with_function, $mt_table_partition_expression_with_function"
+query "DROP TABLE IF EXISTS $mt_table, $s3_table, $mt_table_roundtrip, $s3_table_wildcard, $s3_table_wildcard_partition_expression_with_function, $mt_table_partition_expression_with_function, $mt_alias, $mt_materialized, $s3_alias_export, $s3_materialized_export"
 
 query "CREATE TABLE $mt_table (id UInt64, year UInt16) ENGINE = MergeTree() PARTITION BY year ORDER BY tuple()"
 query "CREATE TABLE $s3_table (id UInt64, year UInt16) ENGINE = S3(s3_conn, filename='$s3_table', format=Parquet, partition_strategy='hive') PARTITION BY year"
@@ -114,4 +119,40 @@ echo "---- Count rows in big_table and big_destination_max_rows"
 query "SELECT COUNT() from $big_table"
 query "SELECT COUNT() from $big_destination_max_rows"
 
-query "DROP TABLE IF EXISTS $mt_table, $s3_table, $mt_table_roundtrip, $s3_table_wildcard, $s3_table_wildcard_partition_expression_with_function, $mt_table_partition_expression_with_function, $big_table, $big_destination_max_bytes, $big_destination_max_rows"
+echo "---- Test ALIAS columns export"
+query "CREATE TABLE $mt_alias (a UInt32, arr Array(UInt64), arr_1 UInt64 ALIAS arr[1]) ENGINE = MergeTree() PARTITION BY a ORDER BY (a, arr[1]) SETTINGS index_granularity = 1"
+query "CREATE TABLE $s3_alias_export (a UInt32, arr Array(UInt64), arr_1 UInt64) ENGINE = S3(s3_conn, filename='$s3_alias_export', format=Parquet, partition_strategy='hive') PARTITION BY a"
+
+query "INSERT INTO $mt_alias VALUES (1, [1, 2, 3]), (1, [10, 20, 30])"
+
+alias_part=$(query "SELECT name FROM system.parts WHERE database = currentDatabase() AND table = '$mt_alias' AND partition_id = '1' AND active = 1 ORDER BY name LIMIT 1" | tr -d '\n')
+
+query "ALTER TABLE $mt_alias EXPORT PART '$alias_part' TO TABLE $s3_alias_export SETTINGS allow_experimental_export_merge_tree_part = 1"
+
+sleep 3
+
+echo "---- Verify ALIAS column data in source table (arr_1 computed from arr[1])"
+query "SELECT a, arr, arr_1 FROM $mt_alias ORDER BY arr"
+
+echo "---- Verify ALIAS column data exported to S3 (should match source)"
+query "SELECT a, arr, arr_1 FROM $s3_alias_export ORDER BY arr"
+
+echo "---- Test MATERIALIZED columns export"
+query "CREATE TABLE $mt_materialized (a UInt32, arr Array(UInt64), arr_1 UInt64 MATERIALIZED arr[1]) ENGINE = MergeTree() PARTITION BY a ORDER BY (a, arr_1) SETTINGS index_granularity = 1"
+query "CREATE TABLE $s3_materialized_export (a UInt32, arr Array(UInt64), arr_1 UInt64) ENGINE = S3(s3_conn, filename='$s3_materialized_export', format=Parquet, partition_strategy='hive') PARTITION BY a"
+
+query "INSERT INTO $mt_materialized VALUES (1, [1, 2, 3]), (1, [10, 20, 30])"
+
+materialized_part=$(query "SELECT name FROM system.parts WHERE database = currentDatabase() AND table = '$mt_materialized' AND partition_id = '1' AND active = 1 ORDER BY name LIMIT 1" | tr -d '\n')
+
+query "ALTER TABLE $mt_materialized EXPORT PART '$materialized_part' TO TABLE $s3_materialized_export SETTINGS allow_experimental_export_merge_tree_part = 1"
+
+sleep 3
+
+echo "---- Verify MATERIALIZED column data in source table (arr_1 computed from arr[1])"
+query "SELECT a, arr, arr_1 FROM $mt_materialized ORDER BY arr"
+
+echo "---- Verify MATERIALIZED column data exported to S3 (should match source)"
+query "SELECT a, arr, arr_1 FROM $s3_materialized_export ORDER BY arr"
+
+query "DROP TABLE IF EXISTS $mt_table, $s3_table, $mt_table_roundtrip, $s3_table_wildcard, $s3_table_wildcard_partition_expression_with_function, $mt_table_partition_expression_with_function, $big_table, $big_destination_max_bytes, $big_destination_max_rows, $mt_alias, $mt_materialized, $s3_alias_export, $s3_materialized_export"