ChatApp - backend

<?php
#define server variable / login info
$servername = "localhost";
$username = "root";
$password = "1234";
$dbname = "apps";

#get variables
$user = $_GET["user"];
$message = $_GET["msg"];

#connect to database
$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}
#listen and reply to client requests
$mode = $_GET["mode"];
if ($mode == "send") {
    $sql = "INSERT INTO chat (user, message)
VALUES ('$user', '$message')";
if ($conn->query($sql) === TRUE) {
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}
}
if ($mode == "get") {
$sql = "SELECT timestamp, user, message FROM chat";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "[" . $row["user"] . "] " . $row["message"];
    }
    } else {
        echo "[Server] Be the first to make a message!";
    }
}
$conn->close();
?>