Make product posts draft if post meta field equals value - sql

Question

I have a function which runs daily which I want to check if a post is expired (based on a custom postmeta field) and if so set the post status to draft. I think I have the principle right but there's something probably pretty wrong with the syntax which isn't making it work correctly. This is the function so far:
function make_product_draft( ) {
global $wpdb;
$sql = "
UPDATE $wpdb->posts
INNERJOIN $wpdb->postmeta on $wpdb->posts.ID = $wpdb->postmeta.post_id
SET $wpdb->posts.post_status = 'draft'
WHERE $wpdb->posts.post_type = 'product' AND $wpdb->posts.post_status = 'publish' AND $wpdb->postmeta.post_type = 'expired'
";
$wpdb->query($sql);
}
I think where I am going wrong is when I do this: $wpdb->posts.ID? I am not sure what the correct syntax is. Your help is much appreciated :)

Answer 1

My requirements changed since I made the post, however the following code worked for me. Thanks Niklaz for the comment, your assistance was pivotal in getting it working right :)
function make_product_draft( ) {
global $wpdb;
$sql = "UPDATE {$wpdb->posts}
INNER JOIN {$wpdb->postmeta} on {$wpdb->posts}.ID = {$wpdb->postmeta}.post_id
SET {$wpdb->posts}.post_status = 'draft'
WHERE {$wpdb->posts}.post_type = 'product' AND {$wpdb->posts}.post_status = 'publish' AND {$wpdb->postmeta}.meta_key = '_product_expiry' AND {$wpdb->postmeta}.meta_value < CURDATE()
";
$wpdb->query($sql);
}