Not updating SQL database - php

Question

For some reason my code isn't updating mySQL database, but it isn't reporting any errors.
register.php (form)
<form class="register_form" action="action.php?do=register" method="post">
Team Name*: <input type="text" name="teamname" required />
Team Region*: <input type="text" name="teamregion" maxlength="4" required />
Team Leader*: <input type="text" name="teamleader" maxlength="16" required />
Team Members: <input type="text" name="teammembers" />
<input name="register_submit" type="submit" value="Register" />
</form>
action.php
<?php
$con=mysqli_connect("192.185.#.###","########_reg","#######","#########");
if (mysqli_connect_errno()) {echo "Failed to connect to MySQL: " . mysqli_connect_error();}
$action = $_GET['do'];
if($action=="register") {
$teamname = $_POST["teamname"];
$teamregion = $_POST["teamregion"];
$teamleader = $_POST["teamleader"];
$teammembers = $_POST["teammembers"];
$result = mysqli_query($con, "INSERT INTO teams (teamname, region, teamleader, teammembers, wins, loses)
VALUES (" . $teamname . "," . $teamregion . "," . $teamleader . "," . $teammembers . ",0,0);");
}
?>
Any ideas why this isn't working correctly?

Answer 1

Here's a working sample with prepared statements, that are "better" to use generally instead of query
action.php
$con = new mysqli('localhost', 'root', '', 'dachi');
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
if (isset($_GET['do']) && $_GET['do'] === "register") {
$teamname = $_POST["teamname"];
$teamregion = $_POST["teamregion"];
$teamleader = $_POST["teamleader"];
$teammembers = $_POST["teammembers"];
$wins = 0;
$loses = 0;
$stmt = $con->prepare("INSERT INTO `teams` (`teamname`,`region`,`teamleader`,`teammembers`,`wins`,`loses`) VALUES (?,?,?,?,?,?)");
$stmt->bind_param('ssssii', $teamname, $teamregion, $teamleader, $teammembers, $wins, $loses);
$stmt->execute();
$stmt->close();
}
register.php
<form class="register_form" action="action.php?do=register" method="post">
Team Name*: <input type="text" name="teamname" required />
Team Region*: <input type="text" name="teamregion" maxlength="4" required />
Team Leader*: <input type="text" name="teamleader" maxlength="16" required />
Team Members: <input type="text" name="teammembers" />
<input name="register_submit" type="submit" value="Register" />
</form>

Answer 2

You should change:
if($action=="register") {
to
if($action=="register_submit") {
Because your input has a tag name set to value register_submit not register.
and change $action = $_GET['do']; to $action = $_POST['register_submit'];

Answer 3

register.php (form)
<form class="register_form" action="action.php?do=register" method="post">
action.php
$action = $_GET['do'];