php /mysql form validation issue - php

Question

so my php validation has two check functions, first it checks for an empty name or password entry and second if user enters unwanted characters while entering his name, the problem is that if the user does enter an unwanted character or numbers in the 'name' entry the form is still saved to the database which it should not, nothing is saved to the database if the users leaves both the name and password field empty and the error is shown, which means half of my validation check is working fine . can any one help me out ?
<?php
// Connect to data base
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "myDB";
// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
// define variables and set to empty values
$nameErr = $userpasswordErr = "";
$name = $userpassword = "";
//check for error
if ($_SERVER["REQUEST_METHOD"] == "POST") {
//validate name and password
if (
empty($_POST["name"]) ||
empty($_POST["userpassword"] ||
!preg_match("/^[a-zA-Z ]*$/",$name))
) {
$nameErr= "* Incorrect username or password ";
} else {
$name = test_input($_POST["name"]);
$userpassword = test_input($_POST["userpassword"]);
$sql = "INSERT INTO users(name,email)
VALUES ('$name','$userpassword')";
if ($conn->query($sql) === true) {
echo "New record created successfully";
} else {
echo "Error: " . $sql . "<br>" . $conn->error;
}
$conn->close();
}
}
function test_input($data) {
$data = trim($data);
$data = stripslashes($data);
$data = htmlspecialchars($data);
return $data;
}
?>
<span class="error"></span>
<form method="post" action="<?php echo htmlspecialchars ($_SERVER["PHP_SELF"]);?>">
name : <input type="text" name="name" value="<?php echo $name;?>"/>
<span class="error"><?php echo $nameErr ;?> </span>
<br/><br/>
password : <input type="text" name="userpassword" value="<?php echo $userpassword ; ?>">
<span class="error"><?php echo $userpasswordErr ;?> </span>
<br/><br/>
<input type="submit" name="submit" value="Submit"/>
</form>

Answer 1

The $name in regular expression check should be $_POST['name']
if(empty($_POST["name"]) || empty($_POST["userpassword"] || !preg_match("/^[a-zA-Z ]*$/",$_POST["name"])))
{
$nameErr= "* Incorrect username or password ";
}