PHP MYSQL: User Delete his own post - php

Question

I have created a forum where people can register/login to post topics and replies.
Now I added a Delete link next to each topic that if pressed will go to deletetopic.php and if the user has created this topic it will be deleted, if not, it will say You Didn't create this topic.
this is the deletetopic.php
<?php
session_start();
include("config.php");
if(!isset($_SESSION['uid'])){
echo "<p><b>ERROR: Please log in to delete a topic.";
}
if(isset($_SESSION['username']))
{
$uid = $_SESSION['uid'];
$id=$_GET['id'];
$query1=mysql_query("delete FROM topics WHERE id='$id' and uid='$uid'");
if($query1){
header('location:index.php');
}
else{
echo "<p><b>ERROR: You didnt make this topic.";
}
}
It doesnt work, it just gives me the else {error}
here are my tables:
CREATE TABLE `users` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`firstname` VARCHAR(255) NOT NULL,
`lastname` VARCHAR(255) NOT NULL,
`email` VARCHAR(255) NOT NULL,
`username` VARCHAR(255) NOT NULL,
`password` VARCHAR(100) NOT NULL,
PRIMARY KEY (`id`)
CREATE TABLE `topics` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`categoryID` TINYINT(4) NOT NULL,
`topicTitle` VARCHAR(150) NOT NULL,
`topicCreator` INT(11) NOT NULL,
`topicLastUser` INT(11) NOT NULL,
`topicDate` DATETIME NOT NULL,
`topicReplyDate` DATETIME NOT NULL,
`topicViews` INT(11) NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
EDIT:
uid comes from here I think: login.php
if (isset($_POST['username'])){
$username = $_POST['username'];
$password = $_POST['password'];
$sql = "SELECT * FROM users WHERE username='".$username."' AND password='".$password."' LIMIT 1";
$result = mysql_query($sql) or die(mysql_error());
if (mysql_num_rows($result) == 1){
$row = mysql_fetch_assoc($result);
$_SESSION['uid'] = $row['id'];
$_SESSION['username'] = $row['username'];
header("Location: index.php");
exit();
}else{
echo "<p>Invalid information. Please return to the previous page.";
exit();
}
}
Update
if(isset($_SESSION['username']))
{
$uid = $_SESSION['uid'];
$id=$_GET['id'];
$check = mysql_query("SELECT * FROM topics WHERE id = '$id' AND topicCreator = '$uid'");
if($check){
$query1=mysql_query("delete FROM topics WHERE id='$id' AND topicCreator='$uid'");
header('location:index.php');
}
else{
echo "<p><b>ERROR: You didnt make this topic.";
}
}
Still doesnt work, just goes back to index

Answer 1

There is no uid column in table topics, it is probably topicCreator:
$query1=mysql_query("delete FROM topics WHERE id='$id' and topicCreator='$uid'");
You should consider the comments left here about changing from mysql to mysqli or PDO. And use of prepared statements to prevent SQL injections.
There is another problem. You need to check if the user is the topicCreator BEFORE deleting the topic.
$check = mysql_query("SELECT * FROM topics WHERE id = '$id' AND topicCreator = '$uid'");
if($check){
// Allow deletion
}
else{
// Don't allow deletion
}