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，如：

+---------+---------------------+----------+----------------------+
| 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是你的朋友。你可以这样做：

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

这样做的方法是添加虚拟列，然后使用分组将它们合并在一起。 e.g。

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
   )
)

这仅适用于您的示例，因为您在查询的每个部分中始终只有一行，否则它根本不起作用。

Answer 3

Union将两个表的结果ROWS添加为一个结果集。 Join将两个或多个表中的COLUMNS作为一行添加。因此，在这种情况下，加入可能是更好的选择。

然而，为了使这项工作，你需要有一些东西可以加入，例如id或确切的日期或类似的东西。因为我不知道你是否有这个是一个示例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。

您是否有可以加入的专栏？

在不同的列中显示union的结果 - mysql

3 个答案: