How to connect node.js to MySQL

Question

I am trying to connect node.js to MySQL and failed. I have installed MySQL and relevant libraries. How do I resolve this error? Also, if I want to get data to react-native, how should I go about doing it?

const express = require('express');
const mysql = require('mysql');

const connection = mysql.createPool({
  host     : '*****',//aws db endpoint/MySQL hostname
  user     : 'administrator', // username of MySQL connection
  password : '*****', //pw of MySQL db
  database : 'database_3' // name of database to be used
});

const app = express();
app.get('/User', function (req, res) {
    connection.getConnection(function (err, connection) {
    connection.query('SELECT * FROM User', function (error, results, fields) {
      if (error) throw error;
      res.send(results)
    });
  });
});

// Starting our server.
app.listen(3306, () => {
    console.log('Go to http://localhost:3306/User');
   });

The error msg received :

events.js:174
      throw er; // Unhandled 'error' event
      ^

Error: listen EADDRINUSE: address already in use :::3306
    at Server.setupListenHandle [as _listen2] (net.js:1279:14)
    at listenInCluster (net.js:1327:12)
    at Server.listen (net.js:1414:7)
    at Function.listen (C:\Users\Irvin\my-new-project\node_modules\express\lib\application.js:618:24)
    at Object.<anonymous> (C:\Users\Irvin\my-new-project\route.js:39:5)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
    at Function.Module._load (internal/modules/cjs/loader.js:585:3)
Emitted 'error' event at:
    at emitErrorNT (net.js:1306:8)
    at process._tickCallback (internal/process/next_tick.js:63:19)
    at Function.Module.runMain (internal/modules/cjs/loader.js:834:11)
    at startup (internal/bootstrap/node.js:283:19)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:622:3)

score 2 · Accepted Answer · answered Dec 17 '19 at 03:01

Error: listen EADDRINUSE: address already in use :::3306

This means that the port 3306 is already in use, try changing it to another port or stop the process running on that port.

// Lets change 3306 to 3307
app.listen(3307, () => {
    console.log('Go to http://localhost:3307/User');
});

If you want to stop the process on this port here is how to do it on linux

score 1 · Answer 2 · answered Dec 17 '19 at 03:31

3306 is the default mysql port. Don't use that port for a server if you already have mysql running.

Don't stop the process on that port otherwise mysql will stop running, unless you're running it in another port, which is not your case.

app.listen(3000, () => {
    console.log('Go to http://localhost:3306/User');
});

score 1 · Answer 3 · answered Dec 17 '19 at 03:31

1

Hi since you are running mysql, it runs on port 3306 by default. Since you are tryung to start your express app on the same port, you get this error. You need to start your express application on any other port.

answered Dec 17 '19 at 03:31

Humblefool

56
4

score 0 · Answer 4 · answered Dec 17 '19 at 03:48

Your nodeJs application is using same port with MySQL .

// Starting our server.
   app.listen(3306, () => {
    console.log('Go to http://localhost:3306/User');
   });

That app.listen(3306) is your nodeJs application listening port, your current MySQL listening port is also 3306 ， so your nodeJs application throw an error

Error: listen EADDRINUSE: address already in use :::3306

Means the port 3306 is already in use . You should change your nodeJs application listening port like 8080 or 8090, For example :

const express = require('express');
const mysql = require('mysql');

const connection = mysql.createPool({
  host     : '*****',//aws db endpoint/MySQL hostname
  user     : 'administrator', // username of MySQL connection
  password : '*****', //pw of MySQL db
  database : 'database_3' // name of database to be used
});

const app = express();
app.get('/User', function (req, res) {
    connection.getConnection(function (err, connection) {
    connection.query('SELECT * FROM User', function (error, results, fields) {
      if (error) throw error;
      res.send(results)
    });
  });
});

// change this port to 8090
app.listen(8090, () => {
    console.log('Go to http://localhost:3306/User');
   });

How to connect node.js to MySQL

4 Answers4