Statistics
https://play.clickhouse.com/play?user=play#c2VsZWN0IAp0b1N0YXJ0T2ZIb3VyKGNoZWNrX3N0YXJ0X3RpbWUpIGFzIGQsCmNvdW50KCksICBncm91cFVuaXFBcnJheShwdWxsX3JlcXVlc3RfbnVtYmVyKSwgIGFueShyZXBvcnRfdXJsKQpmcm9tIGNoZWNrcyB3aGVyZSAnMjAyMi0wNi0wMScgPD0gY2hlY2tfc3RhcnRfdGltZSBhbmQgdGVzdF9uYW1lIGxpa2UgJyUwMjQ5MV9wYXJ0X2xvZ19oYXNfdGFibGVfdXVpZCUnIGFuZCB0ZXN0X3N0YXR1cyBpbiAoJ0ZBSUwnLCAnRkxBS1knKSBncm91cCBieSBkIG9yZGVyIGJ5IGQgZGVzYw==

Some times there are not output from requests.
auto normal_result_ptr = reader.estimateNumMarksToRead(
            normal_parts,
            query_info.prewhere_info,
            required_columns,
            storage_snapshot->metadata,
            storage_snapshot->metadata,
            query_info, 
            added_filter_nodes,
            query_context,
            settings.max_threads,
            max_added_blocks);
        if (normal_result_ptr->error())
            return;
        if (normal_result_ptr->marks() == 0)
            candidate.complete = true;
        else
        {
            sum_marks += normal_result_ptr->marks();
            candidate.merge_tree_normal_select_result_ptr = normal_result_ptr;
        }
    }
    candidate.merge_tree_projection_select_result_ptr = projection_result_ptr;
    
    if (sum_marks < min_sum_marks)
    {
        selected_candidate = &candidate;
        min_sum_marks = sum_marks;
    }
}
Block MergeTreeData::getMinMaxCountProjectionBlock(