While Loop when checking if record exists - PHP

I need to generate a random number. After I generate the number, I need to check my table to see if that number has been generated before. If the random number is not unique, I'll re-regenerate the number until a unique number is generated.

Here is my code:

$con=mysqli_connect($host,$user,$pass,$database);

$random = rand(1000, 9999);

$result = mysqli_query($con,"SELECT * FROM tablex WHERE email = '.$random .'");

$num_rows = mysqli_stmt_num_rows ($result);

while ($num_rows > 0) {

$random = rand(1000, 9999);
$num_rows = mysql_num_rows($result);
 }

$random = rand(1000, 9999);

I need to know if this algorithm is correct - esp. the while loop. Or is there another more efficient way of doing this?