mysql query that joins a parent column and has multiple inner joins - mysql

Question

I'm using the wordpress / woocommerce database structure and am looking to make a custom query.
Basically I need to grab all products without a certain variation and I'm having trouble joining the IDs.
A product and a product_variation are both posts with associated postmeta.
An example schema:
wp_posts wp_postmeta
ID post_id
post_parent meta_key
post_type meta_value
post_status
An example of the wp_posts table would look like this:
id name post_parent meta_key meta_value
2 tshirt null
3 pants null
4 2 variation_type red
5 2 variation_type blue
Here you can see 4 posts; 2 products and 2 variations. The variation's post_parent point to the product. So i have a red and blue tshirt
What I need, is to grab all products with a blue variation, meaning I need to join post_parent to id.
This is what I have so far.
SELECT * FROM wp_posts wp1
INNER JOIN wp_postmeta pm1
ON (pm1.post_id = wp1.ID)
INNER JOIN wp_postmeta pm2
ON (pm2.post_id = wp1.ID)
JOIN wp_posts wp2
ON (wp2.post_parent = wp1.ID)
AND wp1.post_type = 'product_variation'
AND wp1.post_status = 'publish'
AND pm1.meta_key = 'groups-groups_read_post'
AND pm1.meta_value = 'vet_read'
AND pm2.meta_key = 'variation_type'
AND pm2.meta_value = 'blue'
I believe I'm doing the joins wrong. Any guidance is appreciated.

Answer 1

This process is pretty complicated as there are a lot of things going on under the hood. In a project of mine I have to grab all the post ids (primary product ids) based on a certain attribute.
SELECT
DISTINCT p.post_parent FROM `wp_posts` AS p
LEFT JOIN
`wp_postmeta` AS pm ON p.ID = pm.post_id
LEFT JOIN
`wp_postmeta` AS pm2 ON p.ID = pm2.post_id
WHERE
p.post_type = 'product_variation' AND
(
(pm.meta_key = 'attribute_pa_size' AND pm.meta_value = "XL") OR
(pm.meta_key = 'attribute_size' AND pm.meta_value = "XL")
) AND
pm2.meta_key = '_stock' AND pm2.meta_value != '0'
I had a variation size and I wanted to grab the products who have this variation and is of course not out of stock. You will notice I had to check for the meta_key twice because when you enter attribute in product editor page then woocommerce will store it as attribute_{$attribute_name} and save it in the attributes section. But if you select it from the dropdown of available attributes those are saved previously then you have to look for attribute_pa_{$attribute_name}. I am sure you can modify this SQL based on your requirement.
Note: If you intend to use this custom query alongside with the pre_get_posts to set the post__in parameter then regrettably it won't work. Woocommerce has a filter loop_shop_post_in that overrides this. Just to let you know.
Hope this might help you.

Answer 2

I worked it out and this is what I needed
SELECT wp_posts.* FROM wp_posts
INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id)
LEFT JOIN wp_posts p2 ON (wp_posts.ID = p2.post_parent) AND p2.post_type = 'product_variation'
INNER JOIN wp_postmeta pm2 ON (pm2.post_id = p2.ID) AND pm2.meta_key = 'variation_type' and pm2.meta_value = 'blue'
WHERE wp_posts.post_type = 'product'
AND (wp_posts.post_status = 'publish')
AND (wp_postmeta.meta_key = 'groups-groups_read_post')
AND CAST(wp_postmeta.meta_value AS CHAR) = 'vet_read';