javascript张贴到php for mysql插入记录

我读了很多关于这方面的教程，但似乎无法让它发挥作用-我在服务器上有以下PHP文件：

<?php
    $host_name  = "";
    $database   = "";
    $user_name  = "";
    $password   = "";
    $connect = mysqli_connect($host_name, $user_name, $password, $database);
    $user = $_POST['user'];
    $sports = $_POST['sports'];
    $location = $_POST['location'];
    if (mysqli_connect_errno())
    {
        echo "Failed to connect to MySQL: " . mysqli_connect_error();
    }
    $sql = "UPDATE `userActivityLocation` WHERE user='$user' SET sports='$sports', location='$location'";
    $result=mysql_query($sql);
?>

我试了好几种方法都没有用，不知道我做错了什么！如有任何建议，我们将不胜感激，谢谢！

编辑：我已经按照morgeunder的建议尝试了以下操作，但我仍然看不到数据库中创建的任何记录。

这是提交按钮的点击监听器：

$('#register').click(function () {
        console.log("Ready! Getting the user details.");
        username = document.getElementById('login').value;
        password = document.getElementById('password').value;
        email = document.getElementById('email').value;
        window.localStorage.setItem("user", username);
        console.log("Username: ", username);
        console.log("Password: ", password);
        console.log("E-Mail: ", email);
        var params, connection;
        params = {
            login: username,
            password: password,
            email: email
        };
        //console.log("Params: ", params);
        console.log("Creating new user");
        QB.users.create(params, function (err, result) {
            console.log("Result: ", result.toString());
            // callback function
            alert(username.toString());
            var usernamePost = username.toString();
            $.post("http://www.baseurl.co.uk/API/users.php", { user: usernamePost }, function (data) {
                console.log(data);
                console.log("HERE");
            });
            window.location = "sportsSelector.html"
        });
    });