https://pastila.nl/?001ae728/52bc538966a011139c5dac06472b22f6
{
    UInt64 num_rows = data.current_chunk.getNumRows();
    UInt64 num_columns = data.current_chunk.getNumColumns();
    
    UInt64 start = 0;
    
    
    
    
    
    assert(offset < rows_read);
    if (offset + num_rows > rows_read)
        start = offset + num_rows - rows_read;
    else
        return;
    UInt64 length = num_rows - start;
    auto columns = data.current_chunk.detachColumns();
    for (UInt64 i = 0; i < num_columns; ++i)
        columns[i] = columns[i]->cut(start, length);
    data.current_chunk.setColumns(std::move(columns), length);
}
}