Question

[增订]

我有一个表定义的三个表，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 [Regions 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

注意：上面的表格是由PODS CMS plugin在 Wordpress 中创建的，但是简化以使其在此处可读。该实际表格还有数千的数据。

我想做什么

我想列出已定义的相同城市（在本例中为 Albany ）以及区域，因此他们所属的国家。

预期结果：

city    region             country
------- ------------------ --------------
Albany  Western Australia  Australia
Albany  California         United States
Albany  Texas              United States

我尝试过什么

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的区域，但国家/地区不相关。我如何实现上面的样本结果？

先谢谢。

Answer 1

我设法通过两次使用podsrel表获得正确的输出，一次用于城市，一次用于区域。

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

Answer 2

感谢 @sjdaws 的输入，我设法为我的更新问题修改他的解决方案。

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
        AND pr.pod_id = 'pod_3'
        AND pr2.item_id = rg.item_id
        AND pr2.pod_id = 'pod_2'
    ORDER BY co.country, rg.region

在此处查看结果：http://www.sqlfiddle.com/#!2/d40c0/10

MySQL：根据多行数据组合多个相关表

我想做什么

我尝试过什么

2 个答案: