Why isn't my SQL query returning any records?

Question

I'm trying to get the number of records in one of my database tables where the post_id field is equal to the $postID variable I compare it to. When I swap {$postID} out with an integer such as 130 , the query returns results as expected. However, whenever I try to query my DB using the $postID variable, no results are returned. I've checked out what $postID contains to ensure that post_id is being compared to the right value, and it contains an integer value of 130 .

If the query works with a hardcoded 130 in place of $postID , why doesn't it work when I use $postID which is equal to 130 as well?

$postID = get_the_ID();
$postLikes = $wpdb->get_results('
    SELECT COUNT(*) FROM wp_post_likes WHERE post_id = {$postID}
');

echo "<pre>";
     var_dump($postLikes);
echo "</pre>";

Answer 1

Variable substitution does not take place in single quoted strings, see Variable parsing .

And I suggest you use a parameterized query instead of mixing the payload data into the actual statement, see Protect Queries Against SQL Injection Attacks

$postLikes = $wpdb->get_col($wpdb->prepare( 
    'SELECT COUNT(*) FROM wp_post_likes WHERE post_id = %s',
    get_the_ID()
));