Optional Parameters Value

Morning all,

I have a question regarding Optional Parameter Values (Dynamic Parameter).

I have three parameters in my report,

1: Date Range (Start Date to End Date) - This is not optional

2: Customer Account Number - This is an optional value

3: Product Group - This is an optional value

I have setup both 2 and 3 (above) as optional under parameters values however, this does not work properly meaning when I enter a value in Customer Account Parameter it no longer filters the report according to the Customer Account, instead it shows all the records.

My question is, how do you set optional parameter values so when a user enter a value it should filter the data and when user leaves it it should show all the data.

For example

Date: 01-07-2008 to 31-07-2008

Customer Account - None

Product Group - None

Report = All Data within the date range

Date: 01-07-2008 to 31-07-2008

Customer Account: 0010011

Product Group - None

Report = Data according to date range and customer account.

I have setup the parameters under the selection expert like this

{order_header.date_entered} >= {?Start Date:} and
{order_header.date_entered} <= {?End Date:} and
{slcust.slm_custcode} = {?Customer Account Number:} and
{lens_types.prod_group} = {?Product Group:}

though the 2 and 3 option should be optional.

I think I need to change the formula instead of "and" I need something else there but I don't know what. I have read the help file but it doesn't say anything regarding this instead it says, setup the optional under parameters when creating, which I did.

any help will be much appreciated.

Many thanks

Kind Regards

Jehanzeb