MS Query using Parameter in In() statement

[Katie]

I have a query in MS query with three parameters.

One of the parameters needs to allow the user to type in one or multiple
possibilities, or leave it blank for all. I was planning to use the In()
statement: In([Enter Codes here])... which works if I only enter one code,
but not if I enter code,code.

How can I create a parameter in MS Query that allows for the following
situations?

All Values
A list of values
One value.


(Note: this is directly used in the Query, not in VBA)

Thanks