مشکل سرچ در php

سلام

میخاستم سرچ در php رو با pdo انجام بدم ولی با ارور مواجه میشم

<?php 

require('includes/config.php');
$keyword = $_GET['key'];
$min_length = 3;

if(mb_strlen($keyword) >= $min_length){ 
    $stmt = $db->prepare("SELECT FROM blog_posts MATCH (postTitle, postDesc, postCont) AGAINST (:key)");
    $stmt->execute(array('key' => '%'.$keyword.'%'));

    while($row = $stmt->fetchAll(PDO::FETCH_ASSOC)){
        echo $row['postTitle'];
        echo $row['postDesc'];
        echo $row['postCont'];
    }
} else {
    echo 'Cant find! ';
}
?>

<form role="search" method="get" action="http://localhost:8080/Myblog/search.php">
    <div>
        <input type="text" placeholder="Search and hit enter..." name="key">
    </div>
</form>

ارور

PDOStatement->execute(Array) #1 {main} thrown in C:\xampp\htdocs\Myblog\search.php on line 9