在不同的列中显示联合的结果-MySQL

Question

查询

select 
   min(temperature) as minTemp, 
   max(temperature) as maxTemp from test 
union  
( 
   select 
      temperature as Temp , 
      datetime as Date 
   from test 
      order by datetime desc 
   limit 1
) 

返回结果：

+---------+---------------------+
| minTemp | maxTemp             |
+---------+---------------------+
|   24.11 | 26.739999771118164  |
|   25.93 | 2017-05-14 15:11:09 |
+---------+---------------------+

如何在单独的列中显示结果：

+---------+---------------------+----------+----------------------+
| minTemp | maxTemp             |   Temp   |Date                  |
+---------+---------------------+----------+----------------------+
|   24.11 | 26.739999771118164  | 25.93    | 2017-05-14 15:11:09  |
|         |                     |          |                      |
+---------+---------------------+----------+----------------------+

Answer 1

我认为在这种情况下CROSS JOIN是您的朋友。 您可以这样做：

select 
   min(temperature) as minTemp, 
   max(temperature) as maxTemp,
   t.Temp,
   t.Date
from 
    test 
    CROSS JOIN
    (
        select 
          t1.temperature as Temp , 
          t1.datetime as Date 
       from 
          test as t1 
       order by 
          t1.datetime desc 
       limit 1
    ) as t

Answer 2

为此，方法是添加虚拟列，然后使用分组将它们合并在一起。 例如

Select max(minTemp),max(maxTemp),max(Temp),max(Date) from (
   select 
      min(temperature) as minTemp, 
      max(temperature) as maxTemp from test , null as Temp, Null as Date
   union  
   ( 
      select null as minTemp, null as maxtemp,
         temperature as Temp , 
         datetime as Date 
      from test 
         order by datetime desc 
      limit 1
   )
)

这仅在您的示例中有效，因为在查询的每一部分中始终始终只有一行，否则根本行不通。

Answer 3

Union将两个表的结果行添加为一个结果集。 Join将来自两个或多个表的COLUMNS添加为一行。 因此，在这种情况下，加入可能是一个更好的选择。

但是，要使此方法有效，您需要加入一些东西，例如ID或确切日期或类似日期。 由于我不知道您是否有此示例SQL：

select 
min(test1.temperature) as minTemp, 
max(test1.temperature) as maxTemp, 
test2.temperature as Temp, 
test2.datetime as Date 
from test test1 join test test2 
on _something_that_you_can_join_on_ 
order by datetime desc limit 1

test1和test2是我们连接在一起的两个表的别名。

您是否有任何专栏可以加入？