Node.JS-未选择Select Max（）结果

Question

I'm, trying to make a call from my backend where I think I have to use Select MAX(column_name + 1) so that I will have a new value at that column and then show/display it the same time in my front-end.

( I will have to use it to generate a new Order Number )

But the problem is, whenever I call it in my browser to check my output it is not defined. Even in Postman.

I use Node.JS, Express-Generator and React Native

Here is my code

OrderNo.js (models)

var db=require('../dbconnection');

var Task = {
    getTaskById:function(callback){
        return db.query("Select MAX(order_no + 1) from orders",callback,result);
    },
}

module.exports=Task;

OrderNo.js (routes)

var express = require('express');
var router = express.Router();
var Task = require('../models/OrderNo')

router.get('/order_no', (req, res, next) => {
    if(req.params){
        Task.getTaskById(req.params,function(err,rows){    
            if(err)
            {
                res.json(err);
            }
            else{
                res.json(rows);
            }
        });
    }
});

module.exports = router;

The errors:

Answer 1

Your result variable in return db.query("Select MAX(order_no + 1) from orders",callback,result); is not defined in that file. What you're seeing in a javascript execution error as the interpreter fails to find the undefined variable "result", not a MySQL error.