When making a registration and saving information in the database I want to check if the user's email has already been registrated.
function user_id_exists($user){
global $wpdb;
$count = $wpdb->get_var($wpdb->prepare("SELECT COUNT(*) FROM $wpdb->users WHERE ID = %d", $user));
if($count == 1){ return true; }else{ return false; }
}
It should be something like this