I need a formula or maybe SQL that will help me.  I have a parameter set up for Code which can contain multiple values.  I need the code NAT_000 to populate automatically unless a different code is given.  Below is an example of my report.

Day       Advertiser    Code         Time
Monday    Pizza        Nat_000      1:00
Monday    Pizza        CNTY         1:00
Monday    KFC          NAT_000      1:10
Monday    KFC          LOCAL        1:10
Monday    KFC          CNTY         1:10
Monday    Grocery      NAT_000      1:10

If the user enters the parameter of CNTY, I need the report to look like this.  

Day       Advertiser    Code         Time
Monday    Pizza        CNTY         1:00
Monday    KFC          CNTY         1:10
Monday    Grocery      NAT_000      1:10

If the user enter the value of the paramaeter CNTY and LOCAL, if need the report to look like this.

Day       Advertiser    Code         Time
Monday    Pizza        CNTY         1:00
Monday    KFC          LOCAL        1:10
Monday    KFC          CNTY         1:10
Monday    Grocery      NAT_000      1:10

 

Any help would be greatly appreciated!  If you need more info, please let me know.  Thank you!!!!