controller.js

var postModel = require('../models/postModel');
var mysql = require('mysql');
 
// getAall called by routes.js file
app.get('/posts/:username/', [authentication.check, posts.getAll]);
//
 
exports.getAll = function(req, res){
  postModel.findByUsername(req.params.username, function(err, results){
      if(results.length === 0) {
        res.sendStatus(404);
      } else {
        res.json(results);
      }
  });
};

db.js

var db = require('../database');

exports.query =  function(query, cb){
  db.connection_pool.getConnection(function(err, connection) {
    if(err){return cb(err)}
    connection.query(sql, cb);
  });
}

postModel.js

var db = require('../lib/db');
var mysql = require('mysql');

exports.findByUsername = function(username, cb){
  var sql = "SELECT * FROM wall_post WHERE ?? = ?";
  var inserts = ['user_username', username];
  sql = mysql.format(sql, inserts);
  
  db.query(sql, cb);
}