在我不知情的情况下插入了重复值

I have developed one web application by PHP & MySQL. I got an issue part of room allocation module.

In Room Allocation module, User can choose multiple check box (Time slot) depends on their need. In back end, I Collect those time and save into database.

Some times, same data inserted into database twice. It's only occurred some times. Mostly I got proper Output.

My Questions are :

  1. Why It's happening only in some times?
  2. Where duplicate value created?
  3. how it happen?
  4. How to rectify this problem!!

Please some one help me to avoid this problem.!!!

My Insert Coding:

    $admin = $_POST['admin'];

    $roomno = $_POST['str_roomno']; //unique No
    $currentdate = $_POST['str_currentDate'];
    $employeeID = $_POST['str_empID']; //current user ID

    $list_id = $_POST['list'];     //collect list of time slot from previous page
    $total_checkedRows   = count($list_id);   //counting the total slot from previous page



    for($i = 0; $i < $total_checkedRows; $i++)
        {
            $fromTime =  $_POST['time_fromTime'.$list_id[$i]];
            $endTime =  $_POST['time_endTime'.$list_id[$i]];
            $status  = $_POST['str_status'.$list_id[$i]];
            $reason =  $_POST['str_comment'] ; 
            $statusCheck = "occupied";

            if(isset($_POST['id_bookedID'.$list_id[$i]])){
                $id_lineID = $_POST['id_bookedID'.$list_id[$i]];
            }

            if($status == 1)
            {
            $insertSQL = sprintf("INSERT INTO hrms_room_calendar (room_id, booking_date, from_time, to_time, employee_id , booking_status, reason) VALUES (%s, %s, %s, %s, %s, %s, %s)",
                                   GetSQLValueString($roomno, "int"),
                                   GetSQLValueString($currentdate, "date"),
                                   GetSQLValueString($fromTime, "text"),
                                   GetSQLValueString($endTime, "text"),
                                   GetSQLValueString($employeeID, "int"),
                                   GetSQLValueString($statusCheck, "text"),
                                   GetSQLValueString($reason, "text"));

              $Result1 = mysql_query($insertSQL) or die(mysql_error());
            } 
            else if ($status == 2)
            {
                $updateQuery = sprintf("update hrms_room_calendar set booking_status = %s , employee_id = %s, reason = %s where booking_id = %s",
                                   GetSQLValueString($statusCheck, "text"),
                                   GetSQLValueString($employeeID, "int"),
                                   GetSQLValueString($reason , "text"),
                                   GetSQLValueString($id_lineID, "int"));
                $Result1 = mysql_query($updateQuery) or die(mysql_error());
            }

Check Box Coding:

 <form action="BookOrCancel_room.php" method="POST" name="from_roomdetailsfillter" id="from_roomdetailsfillter" onsubmit="return mycommendfunction(1);" >
<input type="hidden" value="<?php echo $_GET['roomid'] ; ?>" name="str_roomno" />
<input type="hidden" value="<?php echo $_GET['calender'] ; ?>" name="str_currentDate" />
<input type="hidden" value="<?php echo $LoginEmpID ; ?>" name="str_empID" />
<input type="hidden"  name="str_comment" id="id_commend" /> <!--value coming from js -->
<input type="hidden" value="<?php echo $admin; ?>" name="admin" />

<?php

foreach($range as $timeRange)  
{ 
        $count ++;
        $fromTime = $timeRange;

        $add_time=strtotime($fromTime)+60;
        $fromTime = date("h:i A", $add_time); //Now starting time + 1 Min


        $Endtime_in_db_24_hour_format = $dbendTime; //Detractly retireve from database

        echo "<input type='text' name='time_fromTime$count' value='$Fromtime_in_24_hour_format' style = 'display: none;'/>
        <input type='text' name='time_endTime$count' value='$Endtime_in_24_hour_format' style = 'display: none;'/> ";

        $link = "BookOrCancel_room.php?roomno=".$roomid."&Currentdate=". $date_Entered. "&employeeID=" . $LoginEmpID . "&fromTime=". $Fromtime_in_24_hour_format."&endTime=".$Endtime_in_24_hour_format;

        if($total_roomdetails > 0)
        { //check initially whether current date atleast once present in database

        //check room already booked or not
        $query_EmpName = sprintf("SELECT * FROM hrms_room_calendar WHERE booking_date = %s and room_id = %s", GetSQLValueString($date_Entered, "date"), GetSQLValueString($roomid, "int"));
        $roomdetails = mysql_query($query_EmpName) or die(mysql_error());

        while($retriveBookedStatus = mysql_fetch_array($roomdetails))
        {

            $db_from_time =  strtotime($retriveBookedStatus['from_time']);
            $local_from_time = strtotime($fromTime);

            if($db_from_time == $local_from_time) 
            {

                $cancelLink = $link."&id=".$retriveBookedStatus['booking_id']."&admin=".$admin;
                echo  "<input type='hidden' name='id_bookedID$count' value=" . $retriveBookedStatus['booking_id']. ">";

                $str_reason = $retriveBookedStatus['reason'];
                $str_cancel_reason = $retriveBookedStatus['cancelled_remarks'];

                   //Display Reason {.............}

                  //Display Employee Name  {.............}

                    if(($status == 2) and ($total_accessdetails_Recordset > 0) and ($date_exited == 0))
                    { //canceled it can book by others
                        $status = 0;
                        //echo "<td style = 'display: none;'><a href=".$cancelLink."&status=2" . " onclick='return confirmCancel();'><input type='button' name='Booked' value='Book'></a></td>";

                        echo "<input type='hidden' value=2 name='str_status$count' />";

                        echo "<td><input type='checkbox' name='list[]' value=$count  id='checkboxbook'  /> <td>";


                    }

            } //if($db_from_time == $local_from_time) 
         }//while

        if($flag != 1) 
        { 
            $flag = 0;

            echo "<tr  height='25' bgcolor='#FFFFFF'>
            <td>";
            echo $fromTime . " - ".$endTime ;
            //Check Whether ending time exited dbEnd Time
            echo TimeExited($Endtime_in_24_hour_format, $Endtime_in_db_24_hour_format );

            echo "</td>";
            echo "<td title='Free'> Available </td>";
            echo "<td align='center'> - </td>";
            echo "<td align='center'> - </td>";
            if(($total_accessdetails_Recordset > 0) and ($date_exited == 0)){ 
            //That particular time and date didnt present in db that is also should not booked
                echo "<td style = 'display: none;'><a href=".$link."&status=1" . " target='_blank'><input type='button' name='Booked' value='Book'></a></td>";
                echo "<input type='hidden' value=1 name='str_status$count' />";

                    echo "<td><input type='checkbox' name='list[]' value=$count id='checkboxbook'  disabled/> <td>";


            } //    if($total_accessdetails_Recordset > 0) 
        } //if($flag != 1)
        else 
        {
            $flag = 0;
        }

    } // if($total_roomdetails > 0)
    else 
    { 

        echo "<tr  height='25' bgcolor='#FFFFFF'>
        <td>";
        echo $fromTime . " - ".$endTime ;
        echo "</td>";
        echo "<td title='Free'>Available </td>";
        echo "<td align='center'> - </td>";
        echo "<td align='center'> - </td>";
        if(($total_accessdetails_Recordset > 0) and ($date_exited == 0)){ //while loading time slot should not booked
            echo "<td style = 'display: none;'><a href=".$link."&status=1" . " target='_blank'><input type='button' name='Booked' value='Book' ></a></td>";
                echo "<input type='hidden' value=1 name='str_status$count' />";

                            echo "<td><input type='checkbox' name='list[]' value=$count id='checkboxbook'  /> <td>";

    }//($total_accessdetails_Recordset > 0)
 } //else
echo "</tr>";
} // foreach
  ?>
   </form>

My Error. It's Only happened some times