节点如果语句未正确触发

Question

我是节点和javascript的完整菜鸟。

我已经设法使用一些教程将下面的脚本拼凑在一起：

//HTTP Server
var app = require('express')();
var http = require('http').Server(app);

//Socket.IO
var io = require('socket.io')(http);

//MSSQL Server
var Connection = require('tedious').Connection;
var Request = require('tedious').Request;  
var Types = require('tedious').Types;  
var config = {userName: '********',  password: '********',server: 'localhost'};  
var connection = new Connection(config); 

//Global
var connectedclients = 0;
var candidatedatenew = "NULL";
var candidatedateold = "NULL";

//Serve Page
app.get('/', function(req, res){
res.sendFile(__dirname + '/Socket.html');
});

//HTTP Server Listen
http.listen(3532, function(){
  console.log('HTTP Server Listening On Port 3532');
});

//Socket Send And Receive
io.on('connection', function(socket){
  connectedclients++;
  console.log(connectedclients);
  socket.on('disconnect', function(){
    connectedclients--;
    console.log(connectedclients);
  });  
  socket.on('chat message', function(msg){
    console.log('message: ' + msg);
    io.emit('chat message');
  });
});

//On MSSQL Server Connect 
connection.on('connect', function(err) {   
    console.log("Connected To MSSQL");  
executeStatement();
    });

//SQL Query
    function executeStatement() {  
        request = new Request("SELECT MAX([datetime]) [datetime] FROM [******].[**].[********];", function(err) {  
        if (err) {  
            console.log(err);}  
        });  
        request.on('row', function(columns) {  
            columns.forEach(function(column) {  
              if (column.value === null) {  
                candidatedatenew = "NULL";
              } else {  
                candidatedatenew = column.value;  
              }
            });  
        });   
        connection.execSql(request);  
    }

//Refresh Query
function sqlRefresh () {
  executeStatement();
  if (candidatedatenew !== candidatedateold) {
  console.log(candidatedatenew);
  console.log(candidatedateold);
  io.emit('refresh');
  candidatedateold = candidatedatenew;
  }
}

setInterval(sqlRefresh, 10000);

麻烦的是，无论值是相同还是不同，我在if语句中的sqlRefresh下的代码似乎都会触发。

这可能是非常简单的事情，但如上所述，我是一个完全新手。