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

Some times there are not output from requests.
auto it = projections.find(candidate.desc->name);
        if (it != projections.end())
            projection_parts.push_back(it->second);
        else
            normal_parts.push_back(part);
    }
    if (projection_parts.empty())
        return;
    auto projection_result_ptr = reader.estimateNumMarksToRead(
        projection_parts,
        candidate.prewhere_info,
        candidate.required_columns,
        storage_snapshot->metadata,
        candidate.desc->metadata,
        query_info,
        added_filter_nodes,
        query_context,
        settings.max_threads,
        max_added_blocks);
    if (projection_result_ptr->error())
        return;
    auto sum_marks = projection_result_ptr->marks();
    if (normal_parts.empty())
    {
        
        
        candidate.complete = true;
    }
    else
    {