express.js with MySQL - mysql

Question

I just started learning node.js...
Here is an example of my code. In this example everything works.
But, I have a question. How to make several SQL queries and send results to template?
At the moment I can only do this for one query...
Thanks.
//connection database
var connection = mysql.createConnection({
host : 'localhost',
user : 'root',
password : 'password',
database : 'test'
});
connection.connect(function (err){
if (err) throw err;
console.log('Database connected . . . \n\n');
});
router.get('/', function(req, res, next) {
var sql = 'SELECT * FROM `test`';
connection.query(sql, function(err, rows, field){
if (err) throw err;
res.render('index', {
data: rows
})
});
});

Answer 1

Here is an answer following my comment since you mentioned you couldn't figure it out on your own.
First snippet uses promises, a quick helper function, but no external library. Second snippet uses the external async.js library and is a bit more callback-heavy. Both of them tackle the problem assuming we want the queries to be executed in parallel.
With promises
router.get('/', async function(req, res, next) {
var queries = ['SELECT * FROM `test`',
'SELECT * FROM `test2`',
'SELECT * FROM `test3`'];
var allResults = [];
/*transform our `query` array into an array of promises, then
await the parallel resolution of all the promises*/
var allQueryRows = await Promise.all(queries.map(query => promiseQuery(query)));
/*'allQueryRows' is an array of rows, so we push each of those
into our results*/
allQueryRows.forEach(function(rows){
allResults.push(...rows);
});
res.render('index', {
data: allResults
})
});
function promiseQuery(sqlQuery){
return new Promise((resolve, reject) => {
connection.query(sqlQuery, function(err, rows, field){
if(err)
return reject(err);
resolve(rows);
})
})
}
With callbacks and async.js
const async = require('async');
router.get('/', function(req, res, next) {
var queries = ['SELECT * FROM `test`',
'SELECT * FROM `test2`',
'SELECT * FROM `test3`'];
var allResults = [];
async.each(queries, function(sqlQuery, callback){
connection.query(sqlQuery, function(err, rows, field){
if(err)
throw err;
allResults.push(...rows);
callback();
});
}, function(){
res.render('index', {
data: allResults
});
});
});