Mysql och node JS = Backend

// Övning med routes     
const express = require('express');
const app = express();
let cors = require('cors');
var mysql = require('mysql');

app.use(express.json());
app.use(cors());
const port = 3001;

let sqlSelect = 'SELECT * FROM data';
let count = 0;
runSQLConn(sqlSelect);
setInterval(runSQLConn, 1000, sqlSelect);
function runSQLConn(sqlSelect) {
    console.log('23');
    count+= 1;
    console.log('Runda:');
    console.log(count);
    
    console.log(sqlSelect);
    console.log('14');

    console.log(sqlSelect);


    var con = mysql.createConnection({
        host: "localhost",
        user: "root",
        password: 'htrhftyjd',
        database: 'scheduleapp'
    });
    con.connect(function(err) {
        if (err) throw err;
        console.log("Ansluten till DB :)");
        //sendSelectToSql(sqlSelect);
        con.query(sqlSelect, function (err, resultToFrontend) {
            console.log(resultToFrontend);
            if (err) throw err;
            // Send the SQL into the Frontend App =============================================================================
            runAppGetRequests(resultToFrontend);
            //return resultToFrontend;
        });
    });
    //con.destroy();
}
app.post('/SQLData/filter', (req, res) => {
    sqlSelect = `SELECT ${req.body.select} FROM data`;
    console.log('49');
    runSQLConn(sqlSelect);

    res.status(201).send();
});
function runAppGetRequests(resultToFrontend) {
    app.get('/SQLData', (req, res) => {
        console.log('56');           
        console.log(resultToFrontend);
        res.status(201).send(resultToFrontend);
    });
    console.log('-----------------------------------');
}
function runAppRequests(resultToFrontend) {
 
}
    /*     function sendSelectToSql(sqlSelect){
        
    } */
//}
/*
function appGet(resultToFrontend){
    console.log('37');
    
} */

app.listen(port, () =>  console.log(`getSQLData is listening on port ${port}!`));