Fix counting column size in wide part for Dynamid and JSON types

src/Storages/MergeTree/MergeTreeDataPartWide.cpp

@@ -108,7 +108,7 @@ ColumnSize MergeTreeDataPartWide::getColumnSizeImpl(
         auto mrk_checksum = checksums.files.find(*stream_name + getMarksFileExtension());
         if (mrk_checksum != checksums.files.end())
             size.marks += mrk_checksum->second.file_size;
-    });
+    }, column.type, getColumnSample(column));
 
     return size;
 }

src/Storages/MergeTree/MergeTreeReaderWide.cpp

@@ -172,7 +172,7 @@ size_t MergeTreeReaderWide::readRows(
                 throw;
             }
 
-            if (column->empty())
+            if (column->empty() && max_rows_to_read > 0)
                 res_columns[pos] = nullptr;
         }
 

tests/queries/0_stateless/03262_column_sizes_with_dynamic_structure.reference

@@ -0,0 +1 @@
+test	10.00 million	352.87 MiB	39.43 MiB	39.45 MiB

tests/queries/0_stateless/03262_column_sizes_with_dynamic_structure.sql

@@ -0,0 +1,22 @@
+-- Tags: no-random-settings
+
+set allow_experimental_dynamic_type = 1;
+set allow_experimental_json_type = 1;
+
+drop table if exists test;
+create table test (d Dynamic, json JSON) engine=MergeTree order by tuple() settings min_rows_for_wide_part=0, min_bytes_for_wide_part=1;
+insert into test select number, '{"a" : 42, "b" : "Hello, World"}' from numbers(10000000);
+
+SELECT
+    `table`,
+    formatReadableQuantity(sum(rows)) AS rows,
+    formatReadableSize(sum(data_uncompressed_bytes)) AS data_size_uncompressed,
+    formatReadableSize(sum(data_compressed_bytes)) AS data_size_compressed,
+    formatReadableSize(sum(bytes_on_disk)) AS total_size_on_disk
+FROM system.parts
+WHERE active AND (database = currentDatabase()) AND (`table` = 'test')
+GROUP BY `table`
+ORDER BY `table` ASC;
+
+drop table test;
+