php - IF NOT EXISTS then INSERT else show message not working -

i have table 'reference' in it, idea if reference exists already, doesn't insert. if doesn't exist insert. code doesn't insert either way. assist please.

$dbconn = pg_connect("host=127.0.0.1 dbname=xx user=xx password=xx") or die('could not connect: ' . pg_last_error()); $query = "if not exists (select reference card reference = '$reference') insert staff (reference, first_name, last_name, address1, address2, address3, address4) values ('$reference', '$first_name', '$last_name', '$address1', '$address2', '$address3', '$address4')";  $result = pg_query($query);     if (!$result)   {   echo "customer update failed!! id might registered us. please go , check spelling of email address.<br><br><input type=\"button\" value=\"go back\" onclick=\"history.go(-1);return true;\">";  die;  } else   {   echo "customer update successful; ";   }    pg_close();  

make column unique. insert , don't worry existence of row. returns false if exists.