如何通过jquery AJAX调用特定的php函数

I have a jquery ajax call to a php file. However, the file contains multiple defined functions, all somewhat similar.

$conn = mysqli_connect($servername, $username, $password, $dbname);


function loadall(){
    $querystring = "SELECT location, filetype, author FROM globalposts ORDER 
BY date DESC";
    $results = mysqli_query($conn, $querystring);

    $row = mysqli_fetch_array($results, MYSQLI_ASSOC);
    echo json_encode($row);
}

function jasperbriggsload(){
    $querystring = "SELECT title, location FROM omar ORDER BY date DESC";
    $results = mysqli_query($conn, $querystring);

    $row = mysqli_fetch_array($results, MYSQLI_ASSOC);
    echo json_encode($row);
}

I have not done overloaded methods with variables, though they might work with my db structure.

My main question is how to call a specific function in an external php through ajax. if I wanted to call loadall() or jasperbriggsload() through just ajax arguments