Question

我正在尝试将delivery表的最新值加入delivery_history表中。为此，我编写了以下查询，但这没有用：

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

我的查询出了什么问题？

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：

如果只希望获得最新状态，则使用相关子查询可能更有效：

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';

Answer 2

使用max

SELECT d.id, max(h.id)
FROM delivery as d
LEFT JOIN delivery_history h ON h.delivery_id = d.id
WHERE h.delivery_status = 'Pending' 
GROUP BY d.id

具有最新值的联接表，无效

2 个答案: