PHP PDO check if data exists not working properly - php

Question

I am working on my blog and I can't seem to figure this out. The if ($result->fetchColumn()) should be working. It does give the error but when data(row) exists it does not show anything. What is wrong?
<?php
$id = $_GET["id"];
$sql = "SELECT * FROM `posts` WHERE `id` = $id";
$result = $conn->query($sql);
if ($result->fetchColumn() > 0) {
while($row = $result->fetch(PDO::FETCH_ASSOC)) {
echo '<div class="post-preview">
<a>
<h2 class="post-title">
'.$row["title"].'
</h2>
<h3 class="post-subtitle">
'.$row["content"].'
</h3>
</a>
<p class="post-meta">'.$row["creator"].' | '.$row["date"].'</p>
</div>
<hr>';
}
}
else {
echo "<center><h1>Post does not exist.</h1></center>";
header("Refresh: 2; url=index.php");
}
?>
Whenever I remove the line if ($result->fetchColumn() > 0) { it works fine. But I need to check if the $id exists in the database. If it does, it should show the data, if not it should show the error and link back to index.php.

Answer 1

Your code could be much simpler
Just populate your $row variable and see whether it contains anything or not.
<?php
$stmt = $conn->prepare("SELECT * FROM `posts` WHERE `id` = ?");
$stmt->execute([$_GET["id"]]); // essential to protect from SQL injection!
$row = $stmt->fetch(PDO::FETCH_ASSOC)
if ($row) {
echo '<div class="post-preview">
<a>
<h2 class="post-title">
'.$row["title"].'
</h2>
<h3 class="post-subtitle">
'.$row["content"].'
</h3>
</a>
<p class="post-meta">'.$row["creator"].' | '.$row["date"].'</p>
</div>
<hr>';
}
else {
echo "<center><h1>Post does not exist.</h1></center>";
header("Refresh: 2; url=index.php");
}