添加LIMIT后，OrderBy查询Php不起作用

I guess my problem is just about a syntax error or SORT BY should come before LIMIT, anyway after adding LIMIT to my query the following statement generates an mysql error.

$query_pag_data = "SELECT * FROM Apartment LIMIT $start, $per_page";// without LIMIT the if statement works while with LIMIT it doesn't.

if ($_GET['SortBy']=="Price" || $_GET['SortBy']=="District" ||) {
$query_pag_data .= "ORDER BY ".$_GET['SortBy']; // It doesn't work if I add LIMIT to my query
}

What is the error and how can I make this working with LIMIT and ORDER BY wout changing my logic.

Your completed SQL should read like SELECT, FROM, ORDER BY, LIMIT. So your PHP should be written like:

$query_pag_data = "SELECT * FROM Apartment";

if ($_GET['SortBy']=="Price" || $_GET['SortBy']=="District") {
    $query_pag_data .= " ORDER BY ".$_GET['SortBy'];
}

$query_pag_data .= " LIMIT $start, $per_page"

this will work

if ($_GET['SortBy']=="Price" || $_GET['SortBy']=="District") {
  $query_order_by= " ORDER BY ".$_GET['SortBy']; 
 }
 $query_pag_data = "SELECT * FROM Apartment $query_order_by LIMIT $start, $per_page";