Merge pull request #11602 from ClickHouse/fix-buffer-sample

Fix buffer sample

src/Storages/StorageBuffer.cpp

@@ -229,6 +229,17 @@ Pipes StorageBuffer::read(
     for (auto & buf : buffers)
         pipes_from_buffers.emplace_back(std::make_shared<BufferSource>(column_names, buf, *this));
 
+    /// Convert pipes from table to structure from buffer.
+    if (!pipes_from_buffers.empty() && !pipes_from_dst.empty()
+        && !blocksHaveEqualStructure(pipes_from_buffers.front().getHeader(), pipes_from_dst.front().getHeader()))
+    {
+        for (auto & pipe : pipes_from_dst)
+            pipe.addSimpleTransform(std::make_shared<ConvertingTransform>(
+                    pipe.getHeader(),
+                    pipes_from_buffers.front().getHeader(),
+                    ConvertingTransform::MatchColumnsMode::Name));
+    }
+
     /** If the sources from the table were processed before some non-initial stage of query execution,
       * then sources from the buffers must also be wrapped in the processing pipeline before the same stage.
       */

tests/queries/0_stateless/01305_buffer_final_bug.sql

@@ -0,0 +1,11 @@
+drop table if exists t;
+drop table if exists t_buf;
+
+create table t (x UInt64) engine = MergeTree order by (x, intHash64(x)) sample by intHash64(x);
+insert into t select number from numbers(10000);
+create table t_buf as t engine = Buffer(currentDatabase(), 't', 16, 20, 100, 100000, 10000000, 50000000, 250000000);
+insert into t_buf values (1);
+select count() from t_buf sample 1/2 format Null;
+
+drop table if exists t_buf;
+drop table if exists t;