3 个表的限价/订单结果

Question

所以我试图将子查询的结果限制为每行一个

    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

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

最后，我想为每个公司获取 company.* 和“最新事件标题”（如果有的话）。

更复杂的是，我很想知道这是否可以通过 Laravel 5.3 的 Eloquent ORM 来完成。

Answer 1

表公司不可见/可用是子查询，因此您有错误，主查询中存在的事实不够。

然后你必须在子查询中加入表公司，例如（我不知道子查询是否适合你的范围）

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，这是您清理的（不正确的）查询：

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;

这（希望）应该是您打算实施的：

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 ，您应该将date与表别名相关联。

祝你好运！