Populating hard coded values for unmatched values between the fields

Populating hard coded values for unmatched values between the fields .

For example:

Below is the table there are values for  Acct_number, portfoilo_number, paid_to_pt_sys_no,portfo_sys_no. 

for desired output table:

for only matched values between the paid_to_pt_sys_no,portfo_sys_no fileds i need get portfoilo_number and for rest i need shown "UNKNOW" . As shown below 

Thanks,