如何將「group by」和max值用於內部連接查詢？

Question

我跟蹤了從3個表中獲取數據的查詢：index_data,data_bin和metrics。

SELECT 
    index_data.host_name,   
    data_bin.value 
FROM 
    metrics 
INNER JOIN 
    index_data ON index_data.id = metrics.index_id 
INNER JOIN 
    data_bin ON data_bin.id_metric = metrics.metric_id 
WHERE 
    metrics.metric_name = 'avg'; 

下面是結果：

host_name  | value 
================================ 
namenode1   1.125 
namenode1   1 
namenode1   1 
namenode1   1 
namenode1   1 
namenode1   4.875 
namenode1   1 
namenode1   0.875 
Centreon-Server  2 
Centreon-Server  1 
Centreon-Server  2 
Centreon-Server  1 
Centreon-Server  5 
Centreon-Server  1 
Centreon-Server  1 
Centreon-Server  2 

我的目標是讓每host_name只有一條記錄，最大value。

所以預期輸出應該是：

namenode1   4.875 
Centreon-Server 5 

我怎樣才能做到這一點？

感謝，

Answer 1

我想下面將幫助您

SELECT 
    index_data.host_name,   
    Max(data_bin.value) as value 
     FROM metrics 
    inner join index_data ON index_data.id = metrics.index_id 
    inner join data_bin ON data_bin.id_metric = metrics.metric_id 

where metrics.metric_name = 'avg' AND 
FROM_UNIXTIME(data_bin.ctime) between date('2014-02-05 16:15:24') and date('2014-02-06 16:15:24') 
Group by index_data.host_name;