how to add a if confition to a mysql query? - php

Question

i am trying to add an if statement to a mysql query so that it checks the user exists from a table called ptb_users in the user_id column before the query runs.
users can write on other users walls and before a user can write on a users wall / before the query inserts into ptb_wallposts, i want it to check that the from_user_id = the ptb_users.user_id.
i am trying to do this but i get syntax errors all over my page can someone please can someone show me how i would need to structure this:
<?php
// check if the review form has been sent
if(isset($_POST['review_content']))
{
$content = $_POST['review_content'];
//We remove slashes depending on the configuration
if(get_magic_quotes_gpc())
{
$content = stripslashes($content);
}
//We check if all the fields are filled
if($_POST['review_content']!='')
{
if exists (select user_id from ptb_users where user_id = #id)
begin
{
$sql = "INSERT INTO ptb_wallposts (id, from_user_id, to_user_id, content) VALUES (NULL, '".$_SESSION['user_id']."', '".$profile_id."', '".$content."');";
mysql_query($sql, $connection);
$_SESSION['message']="<div class=\"infobox-wallpost\"><strong>Wall Post Added</strong> - Your comment was posted to {$profile[2]}'s wall.</div><div class=\"infobox-close4\"></div>";
header("Location: {$_SERVER['HTTP_REFERER']}");
} }
}
end
else
begin
echo "error user doesnt exist"
end
?>

Answer 1

Here's an example of if statement (from MySQL Reference)
IF search_condition THEN statement_list
[ELSEIF search_condition THEN statement_list] ...
[ELSE statement_list]
END IF
Let me explain a little more better, i'll compare between PHP and SQL if statements
PHP:
IF(variable > 0){
anything..
}
SQL:
IF variable > 0 THEN anything..
Read more:MySQL Reference - IF STATEMENT