MySQL：根據多行數據組合多個相關表

Question

[更新]

我有一個表定義的三個表 ，而這三個表之間的關系由另一個表定義，如下所示：

1. 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 

2. 表＃2： wp_pods_regions [地區PODS]

    item_id region -------- ------------------ 1 Western Australia 2 California 3 Texas 4 Bali 

3. 表＃3： wp_pods_countries [國家PODS]

    item_id country -------- -------------- 1 Australia 2 United States 3 Indonesia 

4. 表＃4： wp_posts [帖子類型]

    pod_id pod_name post_type ------- ---------- ---------- pod_1 countries pods pod_2 regions pods pod_3 cities pods 

5. 表＃5： wp_podsrel [PODS關系]

    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：上表是由PODS CMS插件在Wordpress中創建的，但經過簡化后可以在此處讀取。 實際的表也有成千上萬的數據。

我想做什么

我想列出已定義的相同城市 （在本例中為Albany ），以及區域以及它們所屬的國家 。

• 預期結果：

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

我嘗試過的

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

這將使我了解城市及其相關區域，但與國家無關。 我如何獲得上述樣本結果？

提前致謝。

Answer 1

我設法通過兩次使用podsrel表來獲得正確的輸出，一次用於城市，一次用於區域。

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

感謝@sjdaws的輸入，我設法為我更新的問題修改了他的解決方案 。

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

在此處查看結果： http : //www.sqlfiddle.com/#!2/d40c0/10