[已更新]
我有三个表，它们由一个表定义，这三个表之间的关系由另一个表定义，如下所示:
表 #1:wp_pods_cities [城市 PODS]
item_id city -------- ---------- 1 Albany 2 Perth 3 Albany 4 Hollywood 5 Albany 6 San Diego 7 Denpasar表 #2:wp_pods_regions [区域 PODS]
item_id region -------- ------------------ 1 Western Australia 2 California 3 Texas 4 Bali表 #3:wp_pods_countries [国家/地区 PODS]
item_id country -------- -------------- 1 Australia 2 United States 3 Indonesia表 #4:wp_posts [帖子类型]
pod_id pod_name post_type ------- ---------- ---------- pod_1 countries pods pod_2 regions pods pod_3 cities pods表 #5:wp_podsrel [PODS 关系]
rel_id pod_id item_id related_pod_id related_item_id ------- ------- -------- --------------- ---------------- 1 pod_2 1 pod_1 1 2 pod_2 2 pod_1 2 3 pod_2 3 pod_1 2 4 pod_2 4 pod_1 3 5 pod_3 1 pod_2 1 6 pod_3 2 pod_2 1 7 pod_3 3 pod_2 2 8 pod_3 4 pod_2 2 9 pod_3 5 pod_2 3 10 pod_3 6 pod_2 3 11 pod_3 7 pod_2 4
NOTE: The tables above are created in Wordpress by PODS CMS plugin but are simplified to make them readable here. The actual tables also have thousands of data.
我想做什么
我想列出定义的相同城市(在本例中为奥尔巴尼)以及地区，因此< strong>他们所属的国家。
预期结果:
city region country ------- ------------------ -------------- Albany Western Australia Australia Albany California United States Albany Texas United States
我尝试过的
SELECT ct.city, rg.region, ctr.country
FROM wp_pods_cities AS ct
INNER JOIN wp_podsrel AS rel ON ct.item_id = rel.item_id
AND rel.pod_id IN ('pod_3', 'pod_2')
INNER JOIN wp_pods_regions AS rg ON rel.related_item_id = rg.item_id
INNER JOIN wp_pods_countries AS ctr ON rel.related_item_id = ctr.item_id
WHERE ct.city = 'Albany'
ORDER BY ct.city
这将为我提供城市及其相关地区，但国家不相关。如何获得上面的示例结果？
提前致谢。
最佳答案
我成功地通过使用 podsrel 表两次获得了正确的输出，一次针对城市，一次针对地区。
SELECT ct.city, rg.region, co.country
FROM wp_pods_cities AS ct, wp_podsrel AS pr
INNER JOIN wp_pods_regions AS rg
ON rg.item_id = pr.related_item_id
INNER JOIN wp_podsrel AS pr2
ON pr2.item_id = rg.item_id
INNER JOIN wp_pods_countries AS co
ON co.item_id = pr2.related_item_id
WHERE ct.city = 'Albany'
AND pr.item_id = ct.item_id
ORDER BY ct.city
关于MySQL:根据多行数据合并多个相关表，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/15040340/