Question

我有以下结构。不是在一个表中，只是为了保持简单：

Press       | Batch        | Start time
-------------------------------------------------
PRESS_1     | 2051         | 2017-05-18T00:00:00
PRESS_1     | 2052         | 2017-05-19T00:00:00
PRESS_2     | 2053         | 2017-05-20T00:00:00
PRESS_2     | 2054         | 2017-05-16T00:00:00
PRESS_3     | 2055         | 2017-05-12T00:00:00
PRESS_3     | 2056         | 2017-05-18T00:00:00
PRESS_3     | 2057         | 2017-05-19T00:00:00

我想获得每个印刷机的最后计划批次。结果应该是：

Press       | Batch        | Start time
-------------------------------------------------
PRESS_1     | 2052         | 2017-05-19T00:00:00
PRESS_2     | 2053         | 2017-05-20T00:00:00
PRESS_3     | 2057         | 2017-05-19T00:00:00

然而，当我按下分组并且还想选择批次时。我有义务将这批产品放入＆＃39; Group By＆＃39;条款。

Select x.Press, x.Batch, max(x.StartTime)
From myTable x
Group by x.Press

如何使用JPQL实现这一目标？

Answer 1

如果您想选择每次按下最大start_time的条目，您也可以使用下面提到的内容 -

Select x.Press, x.Batch, x.StartTime
From x 
where (press,starttime) in 
(select press, max(starttime) 
from x group by press)

试试看，请告诉我。

Answer 2

您可以使用带有聚合结果的内部联接进行分组

select * from my_table as t1
inner join  (
select Press, max(start_time) my_time
from my_table 
group by Press ) t2 on t1.Press = T2.Press and t2.my_time = t1.start_time

或避免加入

select * from my_table as t1
where (t1.Press, t1.start_time) in (
select Press, max(start_time) 
from my_table 
group by Press )

如果您的ORM有限，您可以创建一个正确的视图，然后使用视图名称作为避免子查询的表

Answer 3

您应该能够从批处理中获得最大值，假设您在每个开始时间批量增加：

Select x.Press, max(x.Batch), max(x.StartTime)
From x
Group by x.Press

在JPQL中选择具有group by和max的行

3 个答案: