mysql - 将表与最新值连接起来，不起作用

Question

我正在尝试将 delivery 表与 delivery_history 表的最新值连接起来。为此，我编写了以下查询，但不起作用:

SELECT d.*
FROM delivery as d
LEFT JOIN 
     (SELECT * 
      FROM delivery_history 
      WHERE delivery_history.delivery_id = d.id 
      ORDER BY id DESC LIMIT 1) h ON d.id = h.delivery_id 
WHERE h.delivery_status = 'Pending' GROUP BY d.id

交货表

id | name  
1  | John

delivery_history 表

id | delivery_id | delivery_status 
1  | 1           | Pending
2  | 1           | Invoiced

预期结果

id | name | delivery_status 
1  | John | Invoiced

我的查询有什么问题？

Answer 1

使用这样的逻辑:

SELECT d.*
FROM delivery d JOIN
     delivery_history dh
     ON dh.delivery_id = d.id JOIN
     (SELECT dh.delivery_id, MAX(dh.id) as max_id
      FROM delivery_history dh
      GROUP BY dh.delivery_id
     ) ddh
     ON ddh.delivery_id = dh.delivery_id AND ddh.max_id = dh.id
WHERE dh.delivery_status = 'Pending';

我将 LEFT JOIN 更改为内部联接，因为您需要匹配 WHERE 条件。

编辑:

如果您只想要最新状态，那么使用相关子查询可能会更有效:

select d.*,
       (select dh.status
        from delivery_history dh
        where dh.delivery_id = d.id
        order by dh.id desc
        limit 1
       ) as latest_status
from delivery d
having latest_status = 'Pending';