Form inserting data duplicate times from all users - php

Question

I can't figure out why, but whenever a user makes a post on the site I am working on it will post to the database multiple times, 1 entry for each member on the site(currently 3).
Here is my code.
Add_topic.php
$category=$_POST['category'];
$sub_category=$_POST['sub_category'];
$topic_data=$_POST['topic_data'];
$posted=date("h:i:s d/m/Y"); //create date time
$sql = "INSERT INTO `topics`(category, sub_category, topic_data, posted_by, posted)VALUES('$category', '$sub_category', '$topic_data', '".$_SESSION['user_id']."', '$posted')";
$result=mysql_query($sql);
if($result){
header("Location: topics.php?category=$category&sub_category=$sub_category");
exit();
}
Topics.php
$sql = "SELECT users.user_id, users.username, users.profile, topics.topic_id, topics.category, topics.sub_category,
topics.topic_data, topics.posted_by, topics.posted, topics.view, topics.reply
FROM users, topics WHERE topics.category = '" . $_GET['category'] . "' AND topics.sub_category = '" . $_GET['sub_category'] . "' ORDER BY topics.posted DESC";
$result = mysql_query($sql);
while($rows = mysql_fetch_array($result)){

Answer 1

I don't think that add_topic.php is inserting multiple rows. You can verify this by looking directly at your table.
I believe your issue is your query in Topics.php.
$sql = "SELECT users.user_id, users.username, users.profile, topics.topic_id,
topics.category, topics.sub_category, topics.topic_data,
topics.posted_by, topics.posted, topics.view, topics.reply
FROM users, topics
WHERE topics.category = '" . $_GET['category'] . "'
AND topics.sub_category = '" . $_GET['sub_category'] . "'
ORDER BY topics.posted DESC";
You are doing a join on users and topics, but you are not defining what links them. So it is creating a row for each user to each topic post.
You can see it as the 1st example result set at this SQLFiddle - http://sqlfiddle.com/#!2/7dfc4/4
What you want to do is LEFT JOIN users to topics ON topics.posted_by = users.user_id.
That is the 2nd example result set at - http://sqlfiddle.com/#!2/7dfc4/4
So your query would now be (escaping your $_GET to prevent SQL Injection) -
$sql = "SELECT users.user_id, users.username, users.profile, topics.topic_id,
topics.category, topics.sub_category, topics.topic_data,
topics.posted_by, topics.posted, topics.view, topics.reply
FROM topics
LEFT JOIN users
ON topics.posted_by = users.user_id
WHERE topics.category = '" . mysql_real_escape_string($_GET['category']) . "'
AND topics.sub_category = '" . mysql_real_escape_string($_GET['sub_category']) . "'
ORDER BY topics.posted DESC";
note - you should not be using mysql_* functions in new code. It is depreciated as of php v.5.5. You should update your code to mysqli_* or PDO. http://php.net/manual/en/mysqlinfo.api.choosing.php