Using a calculated field in a query

Hi,

I have a parameter called Company which is a drop down list for the user to select from. I have also created a calculated field called CompanySelection which looks at what is selected in the parameter and references that value in a field value

=IIFParameters!Company.Value = "Joe Bloggs" then Fields!customer.Value = "11111"

Is there a way I can then add the calculated field to the data source query as a where condition? Something like

Select ZZZ from YYY where AAA between @startdate and @enddate and customer = Fields!customer.Value or something of the sort.

Thanks