Do not return empty blocks from ConvertingAggregatedToChunksTransform (#41152)

* impl

* add test

* update test

src/Processors/Transforms/AggregatingTransform.cpp

@@ -248,8 +248,11 @@ private:
             throw Exception(ErrorCodes::LOGICAL_ERROR, "Some ready chunks expected");
 
         auto & output = outputs.front();
-        output.push(std::move(single_level_chunks.back()));
+        auto chunk = std::move(single_level_chunks.back());
         single_level_chunks.pop_back();
+        const auto has_rows = chunk.hasRows();
+        if (has_rows)
+            output.push(std::move(chunk));
 
         if (finished && single_level_chunks.empty())
         {
@@ -257,7 +260,7 @@ private:
             return Status::Finished;
         }
 
-        return Status::PortFull;
+        return has_rows ? Status::PortFull : Status::Ready;
     }
 
     /// Read all sources and try to push current bucket.
@@ -281,7 +284,10 @@ private:
         if (!two_level_chunks[current_bucket_num])
             return Status::NeedData;
 
-        output.push(std::move(two_level_chunks[current_bucket_num]));
+        auto chunk = std::move(two_level_chunks[current_bucket_num]);
+        const auto has_rows = chunk.hasRows();
+        if (has_rows)
+            output.push(std::move(chunk));
 
         ++current_bucket_num;
         if (current_bucket_num == NUM_BUCKETS)
@@ -291,7 +297,7 @@ private:
             return Status::Finished;
         }
 
-        return Status::PortFull;
+        return has_rows ? Status::PortFull : Status::Ready;
     }
 
     AggregatingTransformParamsPtr params;

tests/queries/0_stateless/02418_do_not_return_empty_blocks_from_ConvertingAggregatedToChunksTransform.reference

@@ -0,0 +1,6 @@
+┌─number─┐
+│     42 │
+└────────┘
+┌─number─┐
+│     42 │
+└────────┘

tests/queries/0_stateless/02418_do_not_return_empty_blocks_from_ConvertingAggregatedToChunksTransform.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+set -ue
+
+unset CLICKHOUSE_LOG_COMMENT
+
+CURDIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+# shellcheck source=../shell_config.sh
+. "$CURDIR"/../shell_config.sh
+
+${CLICKHOUSE_CURL} \
+   $CLICKHOUSE_URL \
+   --get \
+   --data-urlencode "query=
+     select number
+     from numbers_mt(1e6)
+     where number = 42
+     group by number
+     settings max_threads = 10, max_bytes_before_external_group_by = 1, group_by_two_level_threshold = 1
+     format PrettyCompact"
+
+${CLICKHOUSE_CURL} \
+  $CLICKHOUSE_URL \
+  --get \
+  --data-urlencode "query=
+    select number
+    from numbers_mt(1e6)
+    where number = 42
+    group by number
+    settings max_threads = 10, max_bytes_before_external_group_by = 0, group_by_two_level_threshold = 1
+    format PrettyCompact"