select for two conditions on a z table with optional field

Hi.

i have requirement like.

i have to select the data from ztable on the basis of 3 fields out of which one is optional.

need to check if the value comes from this select then read,if no values return,then sleect on the same table removing that 1 optional field,and then check if value is coming.

After getting the data,i have to update the data base table.

please suggest how to make select statements.

thanks inadv