Can you explain a bit ? My code is where to add primary key?

$SQL = “SELECT * FROM jqrgrid_option_tb”;
$result = mysql_query( $SQL ) or die(“Couldn’t execute query.”.mysql_error());
$responce->page = $page;
$responce->total = $total_pages;
$responce->records = $count;
$responces->rows[$i]=PrimaryKey;

$i=0;
while($row = mysql_fetch_array($result,MYSQL_ASSOC)) {
$responce->rows[$i]=$row;
$i++;
}
$json = new Services_JSON();
echo $json->encode($responce);