Question

mysql新手，

在一个表（名为tableX的表）下，假设结构如下所示

server       date           numberofUser
 server1   timestamp        3
 server2   timestamp        2
 server3   timestamp        7
 server1   timestamp        2
 server2   timestamp        8
 server3   timestamp        4

我想收集最后100次出现（所以通过时间戳）但是对于每个时间戳（这意味着对于timestampX（测量所有server1,2,3），我想要服务器1和服务器2的总numberofUser。 / p>

所以欲望输出是

timestamp1     5     (which comes from server1(2)  and server2(3) added
timestamp2     24    (which comes from server1(12) and server2(12) added
timestamp3     7     (which comes from server1(3) and server2(4) added

有人可以指出我正确的方向吗？谢谢

我已经获得了所有服务器（服务器1和2）的最后x次出现的总数，如下所示，但是现在我需要按每个时间戳分解

select sum(numberofUser) from (
    (select  server,   date, numberofUser from tableX 
    where server = 'server1'
    order by date limit 10)
    union
   ( select  server,   date, numberofUser from tableX 
    where server = 'server2'
    order by date limit 10 )) as t

:::::::::::::::::::::::::::::: UPDATE :::::::::::::::: ::

http://sqlfiddle.com/#!9/7bc7f/1

我的计划是

输出我希望看到下面的给定方案

date1                   total
1970-01-01 00:00:03       85
1970-01-01 00:00:04       125

Answer 1

要达到您想要的输出，您必须limit 2而不是您在问题中提到的100。第二个查询在内部使用派生表，首先强制执行最后一个（限制2），外部查询将结果翻转为按照您显示的顺序排序。

select date1,sum(numOfUsers) as total 
from test1 
where server in ('server1','server2') 
group by date1 
order by date1 desc 
limit 2; 
+---------------------+-------+
| date1               | total |
+---------------------+-------+
| 1970-01-01 00:00:04 |   125 |
| 1970-01-01 00:00:03 |    85 |
+---------------------+-------+

您的最终查询是

select date1,total 
from 
(   select date1,sum(numOfUsers) as total 
    from test1 
    where server in ('server1','server2') 
    group by date1 
    order by date1 desc 
    limit 2 
) xDerived 
order by date1; 
+---------------------+-------+
| date1               | total |
+---------------------+-------+
| 1970-01-01 00:00:03 |    85 |
| 1970-01-01 00:00:04 |   125 |
+---------------------+-------+

xDerived只是一个别名。即使之后未明确使用，每个派生表都需要别名。无论它看起来多么愚蠢。

在mysql

1 个答案:

您的最终查询是