Query to Select Appropriate Date Field

Hello,

I am trying to come up with a FMS that selects from three available date fields(Expire Date) based up the Sales Order BP CODE

Sales Order BP Code (Header ORDR.CardCode) UDF Date field 1(Line RDR1.U_Date1) UDF Date field 2(Line RDR1.U_Date2)

UDF Date field 3(Line RDR1.U_Date3

If Sales Order BP Code = ABCD then select UDF Date field 1(Line RDR1.U_Date1)

If Sales Order BP Code = EFGH then select UDF Date field 2(Line RDR1.U_Date2)

If Sales Order BP Code = IJKL then select UDF Date field 3(Line RDR1.U_Date3