Geting records from foreign table

Hi,

I have written function for geting records from table. The function syntax is

$records = $DB->get_records('assignsubmission_file', array('assignment' => $this->get_instance()->importfrom));

This function give me all records from table assignsubmission_file depending on the condition in array. Its okey, but this function also give me records from another table, for examle from table assignsubmission_pdf. It works also conversely, if I get records from asignsubmssion_pdf, it also return records as well from assignsubmission_file table.

Have anybody idea, how it is possible?

Thanks for replies.