Cannot enqueue Handshake after already enqueuing a Handshake - mysql

Question

const app = require('./app');
var mysql = require('mysql');
const server = app.listen(3000, () => {
console.log(`Express is running on port ${server.address().port}`);
});
I learning nodejs 3 day but i don't know how can i fix it i try to fix it but not work.
Someone Help me please
I don't know what i wrong. I want to insert data into mysql with pug
be like login with html and use php to select data in phpmyadmin
register in pug and data send to nodejs and node post data to mysql
I'm sorry my English and gramma so bad :(
const express = require('express');
var mysql = require('mysql');
const router = express.Router();
const app = require('../app.js');
var conn = mysql.createConnection({
host: "localhost",
user: "root",
password: "1234",
database:"project_test"
});
conn.connect(function(err) {
if (err) throw err;
console.log("Index Connection!");
});
conn.connect(function(err) {
if (err) throw err;
console.log("Connected!");
var sql = "INSERT INTO customer (name, address) VALUES ('Company Inc', 'Highway 37')";
conn.query(sql, function (err, result) {
if (err) throw err;
console.log("1 record inserted");
});
});
module.exports = router;