if (isset($var)) { } difficulty using isset

[suckit]

having difficulty using if (isset('prescription')) {'prescription'} in the below code:\[code\]$query = " SELECT id, full_name, address, email, telephone, prescription FROM patients WHERE id LIKE '%" . $patient_id . "%'";\[/code\]problem is that whenever php fetches results from table fields, prescription is sometimes null and sometimes with info.. therefore this notice shows up: Notice: Undefined index: the solutions I'm finding only portray using isset on form inputs rather on data originating from tables. therefore the found examples contain $_POST or $_GET , which don't work for me.cheers,Iain