Ordering results of MySQL query (using join) - mysql

Question

In a WordPress installation, I need to order products so that:
Sold products show up last.
Sold products tagged "antique" show up after sold products tagged "reproduction."
I have successfully completed the first item, but I am at a loss regarding the second item. I'm not getting any errors. My problem is that everything in my ORDER BY statement is working except for "wt.slug DESC." If I change the LEFT JOIN statements for wp_term_taxonomy and wp_terms tables to INNER JOIN statements, I get 0 results, so it looks to me like these statements are not finding the results that I expect. Here is my query:
SELECT SQL_CALC_FOUND_ROWS wp_posts.ID
FROM wp_posts
INNER JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id)
INNER JOIN wp_postmeta ON ( wp_posts.ID = wp_postmeta.post_id )
LEFT JOIN wp_postmeta stock ON ( wp_posts.ID = stock.post_id AND stock.meta_key = '_stock_status' )
LEFT JOIN wp_term_taxonomy wtt ON ( wp_term_relationships.term_taxonomy_id = wtt.term_taxonomy_id AND wtt.taxonomy = 'product_tag' )
LEFT JOIN wp_terms wt ON ( wtt.term_id = wt.term_id AND ( wt.slug = 'antique' OR wt.slug = 'reproduction' ) )
WHERE 1=1
AND ( wp_term_relationships.term_taxonomy_id IN (171) )
AND ( ( wp_postmeta.meta_key = '_visibility' AND CAST(wp_postmeta.meta_value AS CHAR) IN ('visible','catalog') ) )
AND wp_posts.post_type = 'product'
AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private')
GROUP BY wp_posts.ID
ORDER BY wp_posts.post_type DESC, stock.meta_value ASC, wt.slug DESC, wp_posts.post_date
Here is the WordPress database description for reference. I would appreciate any assistance.

Answer 1

You can create a new field as
SELECT SQL_CALC_FOUND_ROWS wp_posts.ID, CASE wt.slug WHEN 'antique' THEN -1 WHEN 'reproduction' THEN 0 ELSE 1 END as sort_order
and use the sort_order in ORDER BY clause like
ORDER BY sort_order DESC

Answer 2

Thanks to help from #mynawaz, I have been able to come up with a solution. I'm not sure if it's the most efficient or elegant solution, but it works:
SELECT SQL_CALC_FOUND_ROWS wp_posts.* , CASE wt.slug WHEN 'antique' THEN 1 WHEN 'reproduction' THEN 2 ELSE 0 END as slug_order
FROM wp_posts
INNER JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id)
INNER JOIN wp_postmeta ON ( wp_posts.ID = wp_postmeta.post_id )
LEFT JOIN wp_postmeta stock ON ( wp_posts.ID = stock.post_id AND stock.meta_key = '_stock_status' )
LEFT JOIN wp_term_relationships wtr ON ( wp_posts.ID = wtr.object_id AND stock.meta_value = 'outofstock' )
LEFT JOIN wp_term_taxonomy wtt ON ( wtr.term_taxonomy_id = wtt.term_taxonomy_id AND wtt.taxonomy = 'product_tag' )
LEFT JOIN wp_terms wt ON ( wtt.term_id = wt.term_id AND wt.slug IN( 'antique','reproduction' ) )
WHERE 1=1
AND ( wp_term_relationships.term_taxonomy_id IN (171) )
AND ( ( wp_postmeta.meta_key = '_visibility' AND CAST(wp_postmeta.meta_value AS CHAR) IN ('visible','catalog') ) )
AND wp_posts.post_type = 'product'
AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private')
AND NOT (
stock.meta_value = 'outofstock'
AND ( CASE wt.slug WHEN 'antique' THEN 1 WHEN 'reproduction' THEN 2 ELSE 0 END ) = 0
)
GROUP BY wp_posts.ID, slug_order
ORDER BY wp_posts.post_type DESC, stock.meta_value ASC, slug_order DESC, wp_posts.post_date DESC