How to make a function to query MySQL in NodeJS? - mysql

Question

I made this:
const mysql = require('mysql2/promise')
const pool = mysql.createPool({
host: 'localhost',
user: 'root',
password: '',
database: 'nodejs',
waitForConnections: true,
connectionLimit: 10,
queueLimit: 0
})
async function query(query) {
const result = await pool.query(query)
return result[0]
}
console.log(query('SELECT * FROM `users`'))
and I got back
Promise { <pending> }
How do I get back my results from querying the database, just like PHP can do?
In PHP I never had to do such a thing like async/await and promises...
I also tried using mysql:
const mysql = require('mysql')
const db = mysql.createConnection({
host : 'localhost',
user : 'root',
password : '',
database : 'nodejs'
})
function query(query) {
db.query(query, (err, result) => {
if (err) throw err
return result
})
}
console.log(query('SELECT * FROM `users`'))
but I got an undefined result

Answer 1

try this:
var mysql = require('mysql');
var con = mysql.createConnection({
host: "localhost",
user: "yourusername",
password: "yourpassword",
database: "mydb"
});
// function definition
function runQuery (con, sqlQuery) {
return new Promise((resolve, reject) => {
console.log("START");
if(con){
con.connect(function (err) {
if (err) throw err;
});
if (sqlQuery) {
con.query(sqlQuery, function (error, result, fields) {
connection.end(); // end connection
if (error) {
throw error;
} else {
return resolve(result);
}
});
} else {
connection.end(); // end connection
// code: handle the case
}
} else {
// code: handle the case
}
});
}
var sqlQuery = 'SELECT * FROM tableName';
// function call and pass the connection and sql query you want to execute
var p = runQuery(con, sqlQuery);
p.then((data)=>{ // promise and callback function
console.log('data :', data); // result
console.log("END");
});

Answer 2

I am not very familiar with MySQL and the libraries that you are using.
However, the Promise { <pending> } response that you are getting is because you didn't await your query execution.
Since the function is marked as async and is also performing an async action, it returns a Promise that needs to be awaited to be resolved.
The code below should work:
const mysql = require('mysql2/promise')
const pool = mysql.createPool({
host: 'localhost',
user: 'root',
password: '',
database: 'nodejs',
waitForConnections: true,
connectionLimit: 10,
queueLimit: 0
})
async function query(query) {
const result = await pool.query(query)
return result[0]
}
(async () => {
const queryResult = await query('SELECT * FROM `users`');
console.log(queryResult);
} )();
To understand how async-await works, consider the code below:
console.log('I will get printed first');
const asyncFunction = async () => {
await setTimeout(()=> {}, 1000)
console.log('I will get printed third');
return 'hello'
}
(async () => {
const result = await asyncFunction();
console.log(`I will get printed last with result: ${result}`);
})();
console.log('I will get printed second');
The console.log statement I will get printed last with result will wait for the asyncFunction to complete execution before getting executed.

Answer 3

Try this:
var mysql = require('mysql');
var con = mysql.createConnection({
host: "localhost",
user: "yourusername",
password: "yourpassword",
database: "mydb"
});
con.connect(function(err) {
if (err) throw err;
con.query("SELECT * FROM customers", function (err, result, fields) {
if (err) throw err;
console.log(result);
});
});