ช่วยแก้ Sub Select Query ใน SQL SERVER หน่อยคะ .................................

SELECT 
     (SELECT COUNT(VN) FROM DNHOSPITAL_TEST.dbo.HNOPD_MASTER 
      WHERE VisitDate BETWEEN '2017-1-1' AND '2017-1-31' AND Cxl='0') as pretotal , 
     (SELECT COUNT(VN) FROM DNHOSPITAL_TEST.dbo.HNOPD_MASTER 
      WHERE VisitDate BETWEEN '2018-1-1' AND '2018-1-31' AND Cxl='0') as total 

function days_in_month($month, $year)
{
     // calculate number of days in a month
      return $month == 2 ? ($year % 4 ? 28 : ($year % 100 ? 29 : ($year % 400 ? 28 : 29))) :(($month - 1) % 7 % 2 ? 30 : 31);
 }   

      $nYear = date('Y');
      $sYear = 2549-543;
    
  for($yy=$nYear;$yy>=$sYear;$yy--) 
  {   
                    
    echo  "<tr>";
    echo  "<td><b>".($yy+543)."</b></td>";

     for($mm=1;$mm<=12;$mm++)
      {
      $dd =cal_days_in_month(CAL_GREGORIAN, $mm, $yy);
       //echo "There was".$dd."days Month".$mm."year".$yy."<br>";
      
       $strSQL="SELECT COUNT(VN) as pretotal, 
           (SELECT COUNT(VN) 
            FROM DNHOSPITAL_TEST.dbo.HNOPD_MASTER 
             WHERE VisitDate BETWEEN '".$yy."-".$mm."-1' AND '".$yy."-".$mm."-".$dd."' AND Cxl='0') as total 
             FROM DNHOSPITAL_TEST.dbo.HNOPD_MASTER 
             WHERE VisitDate BETWEEN '".(($yy)-1)."-".$mm."-1' AND '".(($yy)-1)."-".$mm."-".$dd."' AND Cxl='0'";      

      $objExec = odbc_exec($conn,$strSQL) or die ("Error SQL [".$strSQL."]");
     while($objResult = odbc_fetch_object($objExec))
      {
             $pretotal=$objResult->pretotal; 
             $total=$objResult->total;  
                                    
             //var_dump($pretotal);
             //var_dump($total);
                                    
            $nets= (($total-$pretotal)*100)/$pretotal;
             //echo $nets."<br>";
            echo "<td span class=border>".(number_format($total, 0))."<br>".(number_format($nets, 2))."</td>";
                                    
                                    
 } 
             //echo $strSQL;
     }
           echo "</tr>";
            $yy--;
 }

Warning: odbc_exec(): SQL error: [Microsoft][SQL Server Native Client 11.0][SQL Server]The conversion of a varchar data type to a datetime data type resulted in an out-of-range value., SQL state 22008 in SQLExecDirect in D:\Apache24\htdocs\Bootstrap\ThainakarinStatistics\test\subquery.php on line 34
Error SQL [SELECT COUNT(VN) as pretotal, (SELECT COUNT(VN) FROM DNHOSPITAL_TEST.dbo.HNOPD_MASTER WHERE VisitDate BETWEEN '2016-2-1' AND '2016-2-29' AND Cxl='0') as total FROM DNHOSPITAL_TEST.dbo.HNOPD_MASTER WHERE VisitDate BETWEEN '2015-2-1' AND '2015-2-29' AND Cxl='0']

SELECT 
     (SELECT COUNT(VN) FROM DNHOSPITAL_TEST.dbo.HNOPD_MASTER 
      WHERE Year(VisitDate) = 2017 and month(VisitDate)=1 AND Cxl='0') as pretotal , 
     (SELECT COUNT(VN) FROM DNHOSPITAL_TEST.dbo.HNOPD_MASTER 
      WHERE Year(VisitDate) = 2018 and month(VisitDate)=1 AND Cxl='0') as total