I have a query something like

  //read products with thumbnail and sku
  SELECT products.*, pm1.meta_value as sku, p1.guid as thumbnail
  FROM `wp_posts` as products
  LEFT JOIN `wp_postmeta` as pm1 ON products.product_id = pm1.post_id 
  LEFT JOIN `wp_postmeta` as pm2 ON products.product_id = pm2.post_id 
  LEFT JOIN `wp_posts` as p1 ON pm2.meta_value = p1.ID
  WHERE products.post_type="product" AND pm1.meta_key = '_sku' AND pm2.meta_key = '_thumbnail_id';

This Query will get all the products that have a sku and a thumbnail but will not get any products who are missing a sku or thumbnail.

How do I get all products and the sku if it exists and the thumbnail if it exists?

I do not want to have to run 3 queries and merge the data.