3 個表的限價/訂單結果

Question

所以我試圖將子查詢的結果限制為每行一個

    Tables:    
    Companies: id
    Events: id, title, date
    Relations: local_id, foreign_id

select `companies`.*, `e`.`title` 
from `companies` 
left join (
  select `events`.*, `relations`.`local_id` as `pivot_local_id`, `relations`.`foreign_id` as `pivot_foreign_id` 
    from `events` inner join `relations` on `events`.`id` = `relations`.`foreign_id` 
    where `relations`.`local_id` = companies.id 
    order by `date` desc limit 1 
) e on e.pivot_local_id = companies.id

這個 Q 返回“#1054 - 'where 子句中的未知列'companys.id'”。

最后，我想為每個公司獲取 company.* 和“最新事件標題”（如果有的話）。

更復雜的是，我很想知道這是否可以通過 Laravel 5.3 的 Eloquent ORM 來完成。

Answer 1

表公司不可見/可用是子查詢，因此您有錯誤，主查詢中存在的事實不夠。

然后你必須在子查詢中加入表公司，例如（我不知道子查詢是否適合你的范圍）

select `companies`.*, `e`.`title` 
from `companies` 
left join (
  select `events`.*, `relations`.`local_id` as `pivot_local_id`, `relations`.`foreign_id` as `pivot_foreign_id` 
    from `events` inner join `relations` on `events`.`id` = `relations`.`foreign_id` 
    inner join companies on `relations`.`local_id` = companies.id 
    order by `date` desc limit 1 
) e on e.pivot_local_id = companies.id

Answer 2

所以，這是您清理的（不正確的）查詢：

SELECT c.*, e.title
FROM companies c
LEFT JOIN (
SELECT ev.*, r.local_id AS pivot_local_id, r.foreign_id AS pivot_foreign_id
FROM events ev
INNER JOIN relations r on ev.id = r.foreign_id
WHERE r.local_id = c.id 
ORDER BY `date` DESC LIMIT 1 
) e ON e.pivot_local_id = c.id;

這（希望）應該是您打算實施的：

SELECT c.*, ev.title
FROM companies c
LEFT JOIN relations r ON c.id = r.local_id
LEFT JOIN events ev on ev.id = r.foreign_id
WHERE ev.title IS NOT NULL
ORDER BY `date` DESC LIMIT 1;

注意：您可能不需要WHERE ev.title IS NOT NULL ，您應該將date與表別名相關聯。

祝你好運！