app.get('/some_endpoint', function (req, res) {

    function getData() {
        pool.query('SELECT * FROM users WHERE id = $1', [40], (error, res) => {
            if (error) {
                throw error
            }
            console.log(res.rows[0]); // this logs the correct output
            return res.rows[0];
        });
    }

    let data = getData(); 
    console.log(data);      // this logs undefined
});

I can't get data from the query, for some reason it is undefined sometimes, and sometimes it is not ---0\_/0\_/0---