Functions at Message Mapping - Concatenate with If

Dear SAP Masters, please kindly help me to solve this case.

Please guide me how to achieve this :

Column1 = Sales Order number

Column2 = Sales Order Item number

Column3 = Sales Order Type

Column4 =

For each line, if Column3 start with "ZOR" then column 4 = concatenate Column 1 (SO No) with Column2 (SO Item No), else then Column4 = <blank>

Please kindly give me an idea.

Thanks,

GJ