can lookup be used to match default value in .csv table

I have a csv lookup table with 3 columns, eg: input1,input2,output 240,789,303456 240,330,303457 240,default,303458 246,345,249580 246,330,249589 246,default,230444 The fields to match on input1 and input2 are 3 digit numbers. If input1 matches (240 and 246 in this example) and then input2 matches, then this is a straightforward lookup comand; eg, 240 and 789 will output 303456. But say input1 is 240 and input2 is 389, I need it to match the "240,default,303458" in the table. How can I achieve it in splunk? Thanks.