How can the outside world get values when using nodejs to link MySQL

The code looks like this

 const select = function () {
    let sql = 'SELECT * FROM wdata';
     connection.query(sql,function (err, result) {
        if(err){
          console.log('[SELECT ERROR] - ',err.message);
          return;
        }
       console.log(" The query result is ",result);
    //   return result 
    });
    
};
let data = select()
console.log(data,'data')

Now want to get result The result value returned , How to get it ？

---

Other answers 1：

See what you mean , You want to ask how to get the final result asynchronously ：

You get the result through the callback function ： Change it

const select = function () {
return new Promise(function(resolve, reject){
    let sql = 'SELECT * FROM wdata';
    connection.query(sql,function (err, result) {
        if(err){
            console.log('[SELECT ERROR] - ',err.message);
            reject(err)
            return;
        }
        
        console.log(" The query result is ",result);
    //   return result 
        resolve(result)
    });
})

};

What database do you use for database connection ,Sequelize？ Or what ？
connection.query Look at this API There's no return Promise Of , You can use it directly

const select = async function () {
    let sql = 'SELECT * FROM wdata';
    let res = await connection.query(sql);
    return res;
}

Equivalent to the above writing , But more clearly

Access method 1:

select().then(function(data){
    console.log(data,'data')
}).catch(function(err){
    console.log(err)
})

Access method 2:

async function get(){
    try {
        let data = await select();
        console.log(data,'data')
    } catch (error) {
        console.log(error)
    }
}
get()

Other answers 2：

nodejs Configure the routing , Then request this route at the front end , But you are missing some content here ,nodejs（ I am using express frame ） The last step is to respond the data back to the front end , That is, exposure to the front end , You can get the returned data through the request route , I'll post you a piece of my code ,

Encapsulated operation data file ：

const mysql = require('mysql')
//  Configure the basic parameters of the database 
const conn = mysql.createConnection({
  host: 'localhost', //  Address 
  user: 'root', //  Database user name 
  password: '', //  Database password 
  database: 'BMS_db' //  Database name 
})

//  Connect to database 
conn.connect()

//  Encapsulate the functions that operate the database 
function sqlFn(sql, arr, callback) {
  conn.query(sql, arr, (err, res) => {
    if (err) {
      console.log(err)
      return
    }
    callback(res)
  })
}

module.exports = sqlFn

Routing configuration file ：

const express = require('express')
const router = express.Router()
const sqlFn = require('./mysqlConnect') //  Introduce encapsulated database operation functions 

//  Get all product content 
router.post('/getProducts', (req, res) => {
  const sql = 'select * from product_data'
  sqlFn(sql, null, result => {
    res.send({
      status: 200,
      msg: ' Get all the data ！',
      result
    })
  })
})

Previous code snippet （ I only posted part of my code , The simplest way to query all data ） The operation that finally enables the front end to obtain data in res.send()send Method to pass in an object , All contents in the object can be requested at the front end /getProducts After this route, we get

You need to configure this code later post perhaps get The route of the request , And then use it res( That is to say response) Of send Method to expose the obtained data to the client .

If you don't understand anything else, you can ask again , According to your description, I can only answer so many .