不确定我在这里做错了什么，但我希望在db中添加一行，但只有当该行没有使用该电子邮件地址退出时，请参阅下面的代码：

 function register_user() {
global $wpdb; 
$tablename = $wpdb->prefix."tablename";
$name = $_POST[\'name\'];
$email = $_POST[\'email\'];
$password = $_POST[\'password\'];  


$checkIfExists = $wpdb->get_results("SELECT COUNT(*) FROM tablename WHERE email = $email");
$checkRows = mysqli_num_rows($checkIfExists);

if ($checkRows > 0) {
    header(\'Location: ../register.php?\');
}
else{
$options = [
  \'cost\' => 11,
];
$passwordFromPost = $_POST[\'password\'];
$hash = password_hash($passwordFromPost, PASSWORD_BCRYPT, $options);
$table_name = $wpdb->prefix . "tablename"; 
$wpdb->insert($table_name, array(
  \'name\' => $name, 
  \'email\' => $email,
  \'password\' => $hash
),array(
  \'%s\',
  \'%s\',
  \'%s\') 
);
}

尽管数据库中有电子邮件，但似乎只是我通过了if，直接转到了else。

function register_user() {
    global $wpdb; 
    
    $name = $_POST[\'name\'];
    $email = $_POST[\'email\'];
    $password = $_POST[\'password\'];  

    $checkIfExists = $wpdb->get_var("SELECT ID FROM $wpdb->users WHERE email = \'$email\'");

    if ($checkIfExists == NULL) {

        $userdata = array(
            \'user_login\'    =>  $name,
            \'user_email\'    =>  $email,
            \'user_pass\'     =>  $password,
        );

        $user = wp_insert_user( $userdata );
        
    }
    
}