node查询mysql代码（promise）

var express = require('express');
var router = express.Router();
var mysql = require('mysql');
var cookieParser = require('cookie-parser');
var session = require('cookie-session');
/* GET home page. */
router.get('/', function(req, res, next) {

      function select(sql) {
            var promise = new Promise(function(resolve,reject) {
                var result = null;
                var mysql = require('mysql');
                var connection = mysql.createConnection({
                host: 'localhost',
                user: 'root',
                password: 'root'
                });

                connection.connect();
                connection.query("USE php");//使用php数据库
                connection.query(sql, function (err, results, fields) { 
                    if (err) { 
                        console.log("err");
                        reject(err); 
                    }else {
                        data=[];
                        if(results.length > 0) {
                            for(var i=0;i<results.length;i++){
                                data.push( {
                                    txt: results[i].txt,
                                    content: results[i].content
                                });
                            };
                            //res.write(data);
                            resolve({status:"200",data:data});
                        }else {
                            resolve({status:"500",data:""});
                        }           
                    } 
                } 
                );
                connection.end(); 
            })

            return promise; 
     }
     select("select * from user_n").then(function(data){
            res.json(data);
           res.end();
     }).catch(function(){
          res.json({err:"数据库连接错误!"});
           res.end();
     });

});

module.exports = router;