如何使用相同列但多次關聯不同表來多次連接表？ （MySQL的）

Question

我的場景是一個貨運公司。我有發貨，發件人，收貨人和城市表格。 出貨量表包含shipment_category，sender_id，reciever_id。城市表包含ID和city_name。發件人表保存與城市表ID等同的sender_id，sender_city。 Recievers表包含等於城市表ID的reciever_id和reciever_city。

我設法證明這是屬於組別，並有各城市的ID不同的配位和它們的計數一樣

FROM_CITY出貨量|| To_City || COUNT

1205 || 1346 || 7

我用下面的代碼：

SELECT S.city AS From_City, R.city AS To_City , COUNT(*) 
FROM Shipments Sh, Recievers R, Senders S 
WHERE SH.category=1 
AND SH.sender_id = S.ID 
AND SH.reciever_id = R.ID 
GROUP BY From_City, To_City 
ORDER BY COUNT(*) DESC 

我要的是城市名稱從城市表得到相同的表像下面：

FROM_CITY || To_City ||計數

巴黎||倫敦|| 7

注： 請不建議更改數據庫表。這只是一個示例來表達我的情況。

Answer 1

試試這個：

SELECT 
    `sender_cities`.`city_name` AS `From_City`, 
    `receiver_cities`.`city_name` AS `To_City`, 
    COUNT(*) as `Count` 
FROM 
    `shipments` `ship` 
    INNER JOIN `senders` `s` ON (`ship`.`sender_id` = `s`.`sender_city`) 
    INNER JOIN `cities` `sender_cities` ON (`s`.`sender_city` = `sender_cities`.`city_id`) 
    INNER JOIN `receivers` `r` ON (`ship`.`receiver_id` = `r`.`sender_city`) 
    INNER JOIN `cities` `receiver_cities` ON (`r`.`receiver_city` = `receiver_cities`.`city_id`) 
GROUP BY 
    `From_City`, 
    `To_City` 
ORDER BY 
    `Count` DESC