check where email in present or not in table using php code example

Example: how to ckeck that email is present in databse in mysqli

$select = mysqli_query($connectionID, "SELECT `email` FROM `game` WHERE `email` = '".$_POST['email']."'") or exit(mysqli_error($connectionID));
if(mysqli_num_rows($select)) {
    exit('This email is already being used');
}