var mySql = require("mysql");
var Promise = require("promise");

var pool = mySql.createPool({
  host : "localhost",
  user : "root",
  password : "rahul",
  database : "testDb", //schema
  connectionLimit : 13, // at a time 13 connection be created in pool
});

function getDepartments(){
  return new Promise(fn);

  function fn(resolve,reject){
    pool.getConnection(function(err,con){
        if(err){
            return reject(err);
        }else{
            con.query("select * from departmentTbl",function(err,rows){
                if(err){
                    return reject(err);
                }else{
                    con.release(); // releasing connection to pool
                    return resolve(rows);
                }
            });
        }
      }); // getConnection
    }// fn
 } // getDepartments

getDepartments().then(function(rows){
  console.log(rows);
}).catch(function(err){
  console.log(err);
}).done(function(){
  pool.end();   // closing all connections in pool
});