mysql - SESSION variable in while loop not being sent correctly to second .php file -

i'm trying create simple topic , posting system , have 2 tables in mysql database; topics table , posts table. in posts table have post_parentid field links topic_id field in topics table.

here how start query selecting (and displaying) topics in topic table. save topic_id field variable:

<?php   $sql = "select * topics inner join members on topics.topic_by = members.id";  $topics = $mysqli->query($sql);    if ($topics->num_rows > 0) {   // output data of each topic   while($row = $topics->fetch_assoc()) {   //saving topicid variable    $topic_id = $row["topic_id"];    $_session['topicid'] = $topic_id;?> 

right after display html each topic, start new while loop display each post within each topic:

<?php   $sql = "select * posts inner join members on posts.post_by = members.id post_parentid = $topic_id";  $posts = $mysqli->query($sql);   if ($posts->num_rows > 0) {  // output data of each post  while($row = $posts->fetch_assoc()) { ?> 

right after this, display html each post , display form-control enter post, directed send_post.php file:

 <div class="chat-message-form">   <div class="form-group">    <form action="includes/send_post.php" method="post">      <textarea class="form-control message-input" name="post_content" placeholder="enter message text"></textarea>       <input type="submit">       </form>    </div>  </div> 

when call $topic_id in send_post.php file this:

$topic_id = $_session['topicid']; 

it returns last topic_id in topics table instead of current topic_id in while loop. logic right or should doing different?

by doing in loop:

$_session['topicid'] = $topic_id; 

you're overwriting value of topicid everytime loop. don't know how want topicid possible way avoid be:

$_session['topicid'] = array();  while($row = $topics->fetch_assoc()) { $_session['topicid'][] = $topic_id; ...