PHP MySQL Delete record only if it exist - php

Question

Having a bit of trouble, I have created a form to deleted a record from a linked MySQL database using PHP that works, but I am having an problem with how to make an error display if a uadnumber value for example already exists.
<form name="deleterecord" action="indexdelete.php" method="post">
UAD Username: <br/><input type="text" name="uadnumber" /><br/>
<input type="submit" onclick="return deletedatabase();" value="Delete" />
</form>
<?php
// find the values from the form
$uadnumber = $_POST['uadnumber'] ;
?>
<?php
$con=mysqli_connect($db_hostname,$db_username,$db_password,$db_database);
// Check connection
if (mysqli_connect_errno())
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
$retval = mysqli_query($con,"DELETE FROM users WHERE uadnumber='$uadnumber'");
if(!$retval<0)
{
die('Could not delete data: ' . mysql_error());
}
echo "Deleted all linked data from user $uadnumber successfully"."<br><br>";
echo "<hr>";
echo "Below is the remaining users within the database";
mysqli_close($con);
?>

Answer 1

if (isset($_POST["uadnumber"])) {
$uadnumber = (int)$_POST["uadnumber"];
$db = new mysqli($db_hostname,$db_username,$db_password,$db_database);
if ($db->query("SELECT uadnumber FROM users WHERE uadnumber='".$uadnumber."'")->num_rows > 0) {
if ($db->query("DELETE FROM users WHERE uadnumber='".$uadnumber."'")->affected_rows > 0) {
echo 'Desired rows have been removed.';
} else {
echo 'No rows have been removed.';
}
} else {
echo 'There are no rows identified by given value.';
}
}