表单提交后，PHP会话数据清除

I'm storing session data in $relnum variable, as shown below:

if (!isset($_SESSION)) {
    session_start();
    $_SESSION['releasen'] =$_POST['release_no'];
    $relnum=  $_SESSION['releasen']; 
}

And displaying it in form text field, as shown below;

<input name="relnu" id="relnu" type="text" value="<?php if ($rel==''){ echo $relnum;} else echo $rel; ?>" readonly="true"/>

I am submitting above Form data in mysql, as shown below;

if (isset($_POST['submitM']))  {
    $faultd=$_POST['faultdistribution'];
    $faultdes=$_POST['faultdescription'];
    $faultsev=$_POST['faultseverity'];
    $faultt=$_POST['faulttype'];
    $faultn=$_POST['faultcmnt'];
    $rel=$_POST['relnu'];
    $query = mysql_query("INSERT INTO `fault` (`fault-cmnt`,`fault-type`, `release_no`, `fault-discription`, `fault-severity`, `fault-distribution`) VALUES ('$faultn','$faultt', '$rel', '$faultd', '$faultsev', '$faultdes')")
        or die(mysql_error());
    echo "Data Added sucessfully";
}

The data is successfully submitted, but after that $relnum variable displays nothing. I am unable to comprehend what is the reason, as i am storing the data in session.

P.S: I am not using unset.

Please help, what i am missing?

You have no need to post the session data in the form, else your code seems fine. You can do it easy way with posting it in form like below:

if (isset($_POST['submitM']))  {
    session_start();
    $faultd=$_POST['faultdistribution'];
    $faultdes=$_POST['faultdescription'];
    $faultsev=$_POST['faultseverity'];
    $faultt=$_POST['faulttype'];
    $faultn=$_POST['faultcmnt'];
    $rel=$_SESSION['releasen'];
    $query = mysql_query("INSERT INTO `fault` (`fault-cmnt`,`fault-type`, `release_no`, `fault-discription`, `fault-severity`, `fault-distribution`) VALUES ('$faultn','$faultt', '$rel', '$faultd', '$faultsev', '$faultdes')")
        or die(mysql_error());
    echo "Data Added sucessfully";
}

it will work fine, please test it.

Thank you

Use

session_unset();
session_destroy();

Hope this help

Remember session_start() only store the variable temporary on the server side, check have you session_start() on every page, for checking just echo your session variable on that page, if it did not echo anything then check the previous where from you are making session variable, it can help you sort out your problem by yourself.

You can try below code:

if (isset($_POST['release_no']) && !empty($_POST['release_no'])) {
    session_start();
    $_SESSION['releasen'] =$_POST['release_no'];
    $relnum=  $_SESSION['releasen']; 
}

The session variable is $_SESSION['releasen']. That is what is made available to you every time you have session_start(); at the top of your code. If you want to use $relnum, you'll have to set $relnum equal to $_SESSION['releasen'] on every page load.