Parameter Field value equal to table.field value?

I have create a parameter field in Crystal 8.5 and called it "Customer" and on the Formula field I created a field call "@Custid" and set the value to {sp_billings;1.CustID}. sp_billings is a store procedures. When a user get the Customer prompt how can a user get the customer he specified. Supposed he enter 'ABC' for Customer and I only want him to see the values belong to Customer ABC.below is my code.


select {?Customer}
CASE {?Customer}: ({@Custid}=tek_sp_rpt_billingsALL;1.CustID}{?Customer} and {tek_sp_rpt_billingsALL;1.Vendor} <> '0')

CASE &quot;ALL&quot;: ({@Custid} = {tek_sp_rpt_billingsALL;1.CustID} and {tek_sp_rpt_billingsALL;1.Vendor} <> '0')


The CASE &quot;ALL&quot;:works but not the CASE {?Customer}:. I appreciate somebody can help me. Thanks