如何查询外键并获取相应的行

I have a problem with my PHP query. I just need to get the prescription for the clicked patient in listview.

Here is the table structure for prescription.

I need patient with id 79 to display all his corresponding prescription. Please help me.

Here is the PHP.

<?php

/*
 * Following code will list all the products
 */

// array for JSON response
$response = array();


// include db connect class
require_once __DIR__ . '/db_connect.php';

// connecting to db
$db = new DB_CONNECT();

if (isset($_GET["uid"])) {
    $uid = $_GET['uid'];

// get all products from products table

$result = mysql_query("select * from prescription") or die(mysql_error());

// check for empty result
if (mysql_num_rows($result) > 0) {
    // looping through all results
    // products node
    $response["prescription"] = array();

    while ($row = mysql_fetch_array($result)) {
        // temp user array
        $prescription = array();
        $prescription["pres_id"] = $row["pres_id"];
        $prescription["pres_name"] = $row["pres_name"];
        //$product["price"] = $row["price"];


        // push single product into final response array
        array_push($response["prescription"], $prescription);
    }
    // success
    $response["success"] = 1;

    // echoing JSON response
    echo json_encode($response);
} else {
    // no products found
    $response["success"] = 0;
    $response["message"] = "No prescriptions found";

    // echo no users JSON
    echo json_encode($response);
    } 
}else {
    $response["success"] = 0;
    $response["message"] = "Required field(s) is missing";

    // echoing JSON response
    echo json_encode($response);
}
    }
?>

To get all the prescriptions for a selected patient, wouldn't it be:

mysql_query("select * from prescription where patient_user_fkey = '$patientID'")or die(mysql_error());

instead of:

mysql_query("select * from prescription") or die(mysql_error());