nodejs异步读数据库

function selectUser(callback) {
    var sql = "SELECT * FROM user";

    connection.query(sql, function(err, results) {
        if(!err) {
            callback(res);
        }else {
            callback(error());
        }
}

function query() {
  return new Promise((resolve, reject) => {
    mysql.query($sql, (err, results, fields) => {
      if (err) reject(err);
      mysql.query($sql1, (err, results, fields) => {
        if (err) reject(err);
        resolve(results);
      });
    });
  });
}