How to achieve 'OR' condition between search parameters in program

Hi All,

I have two fields in search parameter let field A and B,   AS per my client requirement , I want result   should search either by A or B  but not both.

I want result  based on 'OR' in between those two parameters.

So suggest me which one going to help me to achieve this by add_selection_param or GET_SELECTION_PARAMS .

And how i write the code for 'OR' Condition.

Can anyone please tell me how can I achieve it ?

Regards

Alok