查找最大查询数（SQL Server 2016）

Question

Q1：如何获得每个虚拟机的NIC数量？ 例如

virtualMachine1  2
virtualMachine2  3
virtualMachine3  1
virtualMachine4  2

Q2：如何获得代表任何虚拟机的最大NIC数量的值？ 例如

10

以下查询返回所有虚拟机网卡对：

SELECT VirtualMachine.VirtualMachineName, VMToNetwork.MacAddress
FROM   VirtualMachine
        INNER JOIN VMToNetwork
         ON VirtualMachine.VirtualMachineID = VMToNetwork.VirtualMachineID 
ORDER BY VirtualMachine.VirtualMachineName

字段“ VMToNetwork.MacAddress”仅用于说明联接有效。

该查询尝试计算每个虚拟机的NIC数量，但只是将NIC的总数相加即可。

SELECT count( VMToNetwork.MacAddress )
FROM   VirtualMachine
        INNER JOIN VMToNetwork
          ON VirtualMachine.VirtualMachineID = VMToNetwork.VirtualMachineID 

谢谢。

Answer 1

添加group by子句，它将计算每个计算机名称唯一的值：

SELECT VirtualMachine.VirtualMachineName, count( VMToNetwork.MacAddress )
FROM   VirtualMachine
        INNER JOIN VMToNetwork
          ON VirtualMachine.VirtualMachineID = VMToNetwork.VirtualMachineID
        GROUP BY VirtualMachine.VirtualMachineName 

Answer 2

要获取每个VM的NIC数量，必须按VM名称分组：

SELECT VirtualMachine.VirtualMachineName, count(VMToNetwork.MacAddress) as NICCount
FROM VirtualMachine
INNER JOIN VMToNetwork ON VirtualMachine.VirtualMachineID = VMToNetwork.VirtualMachineID
GROUP BY VirtualMachine.VirtualMachineName

要从中获得最大收益，您可以按NICCount排序并获得最高价：

SELECT TOP 1 VirtualMachine.VirtualMachineName, count(VMToNetwork.MacAddress) as NICCount
FROM VirtualMachine
INNER JOIN VMToNetwork ON VirtualMachine.VirtualMachineID = VMToNetwork.VirtualMachineID
GROUP BY VirtualMachine.VirtualMachineName
ORDER BY NICCount

请注意，在平局中，您只会得到一名平局成员。

如果只需要最大NIC数，也可以使用子查询：

SELECT MAX(T1.NICCount)
FROM (
    SELECT count(VMToNetwork.MacAddress) as NICCount
    FROM VirtualMachine
    INNER JOIN VMToNetwork ON VirtualMachine.VirtualMachineID = VMToNetwork.VirtualMachineID
    GROUP BY VirtualMachine.VirtualMachineName
) as T1