node mysql sequential query execution

Question

I am trying to fetch some results and do the further processing based on those results, but I can't proceed to work it sequentially,

var sql = query1;

    con.query(sql, function (err, results) {
      if (err) throw err;
     //  ids => 5,2,3,4
      for (i = 0; i < results.length; i++) {

        target_user = results[i].ID

        var sql = "DELETE QUERY";

        con.query(sql, function (err) {
          if (err) throw err;
          console.log(target_user)

          var sql = "INSERT QUERY";
          console.log(sql)
          con.query(sql, function (err) {
            if (err) throw err;

          })
        })


      }
    })

The above code runs asynchronously, What I expect is an output in a loop like this

// "DELETE QUERY";
//5
// "INSERT QUERY";
// "DELETE QUERY";
//2
// "INSERT QUERY";

and so on..

but what I get is

// "DELETE QUERY";
//5
// "DELETE QUERY";
//5 //not fetching the next array val
// "INSERT QUERY";
// "INSERT QUERY";

Any help is much appriciated.

---

EDIT

from answers I updated code like this

now the code looks like this

 aysnc.forEach(results, function(elem, callback){
target_user = elem.id
   console.log('out')
                    console.log(target_user)
                    con.query(sql, function (err) {
                      if (err) throw err;
                      console.log('in')
                    console.log(target_user)
})
})

A strange thing happened that output is

out
5
in
5
out
2
in
5 //when it is supposed to be 2

Answer 1

You could use recursion to solve something like this. Keep calling function until there is no elements left in results

con.query(sql, function (err, results) {
  if (err) throw err;
  deleteAndInsertResults(results);
})

function deleteAndInsertResult(results)
{
    target_user = results[0].ID

    var sql = "DELETE QUERY";

    con.query(sql, function (err) {
      if (err) throw err;
      console.log(target_user)

      var sql = "INSERT QUERY";
      console.log(sql)
      con.query(sql, function (err) {
        if (err) throw err;
        results.shift();
        if(results.length){
          return deleteAndInsertResult(results);
        }

      })
    })
}

Answer 2

In node.js FOR loop will be executed parallely, so use async module or PROMISE below is an example using async

var async = require('aynsc');
con.query(sql, function (err, results) {
  if (err) throw err;
 //  ids => 5,2,3,4
async.forEach(results, function(elem, callback){  

    target_user = results[i].ID

    var sql = "DELETE QUERY";

    con.query(sql, function (err) {
      if (err) throw err;
      console.log(target_user)

      var sql = "INSERT QUERY";
      console.log(sql)
      con.query(sql, function (err) {
        if (err) throw err;
         callback()
      })
    })
}, function(err){
//final callback once loop is done
});
})

Answer 3

You can still use npm module async in a different way

const mysql = require('mysql');
const async = require('aynsc');

var db; //database variable
async.series([
  //creates DB connection and connects
  function(callback){
    db = mysql.createConnection(DB_INFO); //DB_INFO is an Object with information on the BD to be connected

    db.connect(function(err){
      if (err) {
        console.error('error connecting: ' + err.stack);
        return;
      }
      callback(); //goes to the next function
    }); 
  },

  //performs the Query 1
  function(callback){
    db.query('QUERY1', function(){
      callback(); //goes to the next function
    });    
  },

  //performs the Query 2 only after Query 1 is finished
  function(callback){
    db.query('QUERY2', function(){
      db.end(); //closes connection
      callback();
    });    
  }
]);