MySQL：根据多行数据组合多个相关表

Question

[UPDATED]

I have three tables that are defined by one table and the relationship between those three tables are defined by another table like below:

1. Table #1: wp_pods_cities [Cities PODS]

    item_id city -------- ---------- 1 Albany 2 Perth 3 Albany 4 Hollywood 5 Albany 6 San Diego 7 Denpasar 

2. Table #2: wp_pods_regions [Regions PODS]

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

3. Table #3: wp_pods_countries [Countries PODS]

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

4. Table #4: wp_posts [Post Types]

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

5. Table #5: wp_podsrel [PODS Relationship]

    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.

What I'd Like To Do

I would like to list the same cities which are defined (in this case, Albany ) as well as the regions and thus the countries they belong to.

• expected result:

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

What I've Tried

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

This will get me the cities and their related regions but the countries aren't related. How do I achieve the sample result above?

Thanks in advanced.

Answer 1

I managed to get the correct output by using the podsrel table twice, once for city, once for region.

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

Thanks to @sjdaws 's input I managed to modify his solution for my updated question.

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

Check out the result here: http://www.sqlfiddle.com/#!2/d40c0/10