问如何将刚刚通过自动增量插入的外键引用到两个插入查询

EN

TBLTHREAD
* thread_id
* user_id
* date_posted
* thread_title

TBLPOST
* post_id
* thread_id (FK)
* user_id
* date_posted
* post_message

    <form method="post" action="new_thread_result.php" target="_self">
    <table>

    <tr>
    <td>Title:</td>
    <td><input type="text" name="title" required></td>
    </tr>

    <tr>
    <td>Message:</td>
    <td><textarea name="message" cols="30" rows="10" required></textarea></td>
    </tr>

    <tr>
    <td colspan="2"><center><input type="submit" name="submit" value="Submit"></center></td>
    </tr>
    </table>

    </form>

$query="INSERT INTO tblthread (user_id, thread_title, thread_status) VALUES ('$_SESSION[id_ni_user]','$_POST[title]','$status')";
$result=mysql_query($query,$db) or die (mysql_error($db));