您可以通过加入 wp_postmeta 两次来做到这一点，一次针对国家/地区，一次针对注册:

You can do this by joining to wp_postmeta twice, once for the country and once for the registrations:

SELECT date(p.post_date) as Date, pmc.meta_value as Country,
       SUM( pmr.meta_value = 'online' ) as num_online,
       SUM( pmr.meta_value = 'offline' ) as num_offline
 FROM wp_posts p INNER JOIN
      wp_postmeta pmc 
      ON pmc.post_id = p.id AND
         pmc.meta_key = 'country_id' LEFT JOIN
      wp_postmeta pmr
      ON pmc.post_id = p.id AND
         pmc.meta_key = 'registion_by' 
WHERE p.post_type = 'institute' AND
      p.post_status = 'publish'
GROUP BY date, country;