WooCommerce empty sku check

gistfile1.txt

 SELECT p.ID, 
	      p.post_title, 
	      p.post_type, 
	      pm.meta_value
     FROM wp_posts p
LEFT JOIN wp_postmeta pm
       ON pm.post_id = p.ID
      AND pm.meta_key = '_sku'
    WHERE p.post_type = 'product'
      AND (pm.meta_value = '' 
       OR pm.meta_value IS NULL);