How to find and delete orphaned product variations from WooCommerce sites.

delete.sql

DELETE o FROM `wp_posts` o
LEFT OUTER JOIN `wp_posts` r
ON o.post_parent = r.ID
WHERE r.id IS null AND o.post_type = 'product_variation'

select.sql

SELECT * FROM `wp_posts` o
LEFT OUTER JOIN `wp_posts` r
ON o.post_parent = r.ID
WHERE r.id IS null AND o.post_type = 'product_variation'

Old post but it's the one I found. As an update to this, I believe you should also delete the associated postmeta rows. here's the query I used:

delete v, pm
from wp_posts v
left join wp_postmeta pm on (pm.post_id = v.id)
left join wp_posts p on (v.post_parent = p.id)
where v.post_type = 'product_variation' and p.id is null

Now we have a built in WooCommerce option for this as described here: https://stackoverflow.com/a/46245440/1788684

WP Admin > Woocommerce > Status > Tools tab > Delete Orphaned variations