From 8cd841c4acd6ea8aeee33ab21ac0c9c2c1245f0e Mon Sep 17 00:00:00 2001
From: vdimir <vdimir@yandex-team.ru>
Date: Fri, 2 Apr 2021 16:55:42 +0300
Subject: [PATCH] Handle lowcardinality block in MergeJoin extractMinMax

---
 src/Interpreters/MergeJoin.cpp | 9 +++++----
 src/Interpreters/MergeJoin.h   | 3 +++
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/Interpreters/MergeJoin.cpp b/src/Interpreters/MergeJoin.cpp
index ddeaf053225..e9d1eafbdb9 100644
--- a/src/Interpreters/MergeJoin.cpp
+++ b/src/Interpreters/MergeJoin.cpp
@@ -86,10 +86,10 @@ Block extractMinMax(const Block & block, const Block & keys)
 
     for (size_t i = 0; i < columns.size(); ++i)
     {
-        const auto & src_column = block.getByName(keys.getByPosition(i).name);
-
-        columns[i]->insertFrom(*src_column.column, 0);
-        columns[i]->insertFrom(*src_column.column, block.rows() - 1);
+        const auto & src_column = block.getByName(min_max.getByPosition(i).name);
+        /// Cannot use insertFrom because src_column type can differ from keys, e.g. to be LowCardinality
+        columns[i]->insert((*src_column.column)[0]);
+        columns[i]->insert((*src_column.column)[block.rows() - 1]);
     }
 
     min_max.setColumns(std::move(columns));
@@ -485,6 +485,7 @@ MergeJoin::MergeJoin(std::shared_ptr<TableJoin> table_join_, const Block & right
             left_blocks_buffer = std::make_shared<SortedBlocksBuffer>(left_sort_description, max_bytes);
 }
 
+/// Has to be called event totals is empty
 void MergeJoin::setTotals(const Block & totals_block)
 {
     totals = totals_block;
diff --git a/src/Interpreters/MergeJoin.h b/src/Interpreters/MergeJoin.h
index a13d0304907..d145a69ce9d 100644
--- a/src/Interpreters/MergeJoin.h
+++ b/src/Interpreters/MergeJoin.h
@@ -76,12 +76,15 @@ private:
     Block right_table_keys;
     Block right_columns_to_add;
     SortedBlocksWriter::Blocks right_blocks;
+
+    /// Each block stores first and last row from corresponding sorted block on disk
     Blocks min_max_right_blocks;
     std::shared_ptr<SortedBlocksBuffer> left_blocks_buffer;
     std::shared_ptr<RowBitmaps> used_rows_bitmap;
     mutable std::unique_ptr<Cache> cached_right_blocks;
     std::vector<std::shared_ptr<Block>> loaded_right_blocks;
     std::unique_ptr<SortedBlocksWriter> disk_writer;
+    /// Set of files with sorted blocks
     SortedBlocksWriter::SortedFiles flushed_right_blocks;
     Block totals;
     std::atomic<bool> is_in_memory{true};