Question

我尝试为每个WorkOrder选择最新的Customer。我已使用ORDER BY和GROUP BY，但返回的结果不是最新的WorkOrder。

表格结构：

WorkOrder
    id
    customer_id
    create_date
    ...

示例数据：

WorkOrder.id    WorkOrder.customer_id   WorkOrder.create_date   ...
1               1                       2012-01-01 12:00:00
2               1                       2016-06-29 12:00:00
3               2                       2015-05-05 12:00:00

期望的结果：

WorkOrder.id    WorkOrder.customer_id   WorkOrder.create_date   ...
2               1                       2016-06-29 12:00:00
3               2                       2015-05-05 12:00:00

当前代码：

$query = DB::table('WorkOrder')
    ->orderBy('WorkOrder.create_date', 'desc')
    ->groupBy('WorkOrder.customer_id');

// select * from `WorkOrder` group by `WorkOrder`.`customer_id` order by `WorkOrder`.`create_date` desc

当前结果：

WorkOrder.id    WorkOrder.customer_id   WorkOrder.create_date   ...
1               1                       2012-01-01 12:00:00
3               2                       2015-05-05 12:00:00

Answer 1

使用最大功能

SELECT WorkOrder.id, WorkOrder.customer_id, MAX(WorkOrder.create_date) FROM `WorkOrder` GROUP BY `WorkOrder`.`customer_id` ORDER BY `WorkOrder`.`create_date` DESC

Answer 2

试试这个：

SELECT * FROM WorkOrder 
WHERE (customer_id, create_date) IN 
      (SELECT customer_id, MAX(create_date) FROM WorkOrder
       GROUP By customer_id)
ORDER BY ...

Answer 3

我倾向于使用相关子查询来执行此操作：

select wo.*
from workorder wo
where create_date = (select max(wo2.create_date)
                     from workorder wo2
                     where wo2.customer_id = wo.customer_id
                    );

这种方法优于在子查询中使用group by：

如果where子句中有其他过滤器，则只会在减少的行集上查找值。
它可以使用索引进行查找，而无需先进行聚合。

每个唯一列值限制一行，按最大列值选择

3 个答案: