Question

I’m having some difficulty with my SQL statement. I’m doing a query on WordPress to display posts based on multiple post meta fields. When I do the query and filter with only one meta field, or a OR on multiple it works, however AND on multiple fails.

SELECT wposts . *
FROM wp_posts wposts
INNER JOIN (
  SELECT post_id
  FROM wp_postmeta wpostmeta
  WHERE (
    (wpostmeta.meta_key = 'ulnooweg_business_industry'
      AND wpostmeta.meta_value = 'Legal Services')
    AND (
    wpostmeta.meta_key = 'ulnooweg_business_province'
      AND wpostmeta.meta_value = 'New Brunswick')
  )
  GROUP BY post_id
) 
AS t ON t.post_id = wposts.ID
WHERE wposts.post_status = 'publish'
AND wposts.post_type = 'business'
ORDER BY wposts.post_title ASC
LIMIT 0 , 30 

Answer 1

Your query is testing if meta_key (and meta_value) is 2 different values in the same row, which is impossible. But I see what you are trying to do..

Try joining the wp_postmeta table twice except each with an ON clause that excludes all rows except those that satisfy the meta_key condition:

SELECT 
    p.*, 
    GROUP_CONCAT(CONCAT(pm.meta_key,':',pm.meta_value) SEPARATOR ',') AS meta_values
FROM 
    wp_posts p
    JOIN wp_postmeta pm ON pm.post_id = p.ID
    JOIN wp_postmeta pm_bi ON (pm_bi.post_id = p.ID AND pm_bi.meta_key = 'ulnooweg_business_industry')
    JOIN wp_postmeta pm_bp ON (pm_bp.post_id = p.ID AND pm_bp.meta_key = 'ulnooweg_business_province')
WHERE 
    pm_bi.meta_value = 'Legal Services'
    AND pm_bp.meta_value = 'New Brunswick'
    AND p.post_type = 'business'
    AND p.post_status = 'publish'
GROUP BY p.ID
ORDER BY p.post_title ASC

Note: I joined the wp_postmeta table 3 times here to help prove that the conditions are satisfied, but you can remove the GROUP_CONCAT line (and the comma on the previous line of course) and the first JOIN to wp_postmeta and the query will work the same.