Replace values on relashionship

Hi,

I created a relation between 2 tables. Table A contains 2 fields: User Name / Request ID. Table B contains 1 field: User Name (distinct)

The relation works fine and I'm getting Table C with 3 columns: User Name (from Table A) / Request ID / User Name (from Table B).

Is there any way I can change the value of the User Name on Table 3 to YES/NO meaning YES = when the User Name exists and NO when User Name is blank?

Thanks,

Ezequiel