const insertUser = (userData, callback) => {
  const sql = 'INSERT INTO glb_user SET ?';
  db.query(sql, userData, (err, results) => {
    if (err) {
      console.error('Error inserting user:', err.message);
      return callback(err, null);
    }
    console.log('User inserted with ID:', results.insertId);
    callback(null, results);
  });
};