Lost records in Access query, null val.

When running a multiple table query in Access 2000, I would like to display query results that have a null value. By default, Access skips null value results. For example, a table of doctors and a table of patient is queried to see how many patients per doctor in a certain time period. If a particular doctor has patients in June, he will show up in a query of June patients. If he has NO patients in July, he won’t show up as a record in the July query (a null value result). How can I get thequery to display this type of null value?