how to select the field that is not empty?

i want to select the 'operasi 'field that is not empty. how was the query?is it like below. i try like that but error.Anyone can help me?

$sql="SELECT ID,NamaPeralatan,Jenama,Operasi FROM listofitem WHERE NamaPeralatan LIKE '%$search%'AND Operasi is NOTNULL";