sql-server - 具有选择和空检查的情况

Question

select a.AgentId,
       case(select acs.IsConnected
            from rmm.tblAgentConnectionStatus acs
            where acs.AgentName = a.AgentName)
        when 1 then 'True'
        when 0 then 'False'
        when null then 'False'
        end as ConnectionStatus
from Sentilan2.rmm.tblAgent a
order by AgentName asc

我有上述内容，但当它们在tblAgent中没有相应的行时，它会导致ConnectionStatus为空。

当列为空时，结果是否可能为False。

电流输出

AgentId                                 ConnectionStatus
010D0206-5D8C-4AB1-90B6-7BD0C2773E22    True
CA4C48DD-3D2E-4948-9F93-254CDF081658    True
1DB90EE5-D96A-4071-8F51-26B3130EC6D4    NULL
ACA694D0-0C1D-45BA-80DD-273F41BD70B1    NULL
941B539B-7CA0-4472-ABCD-2777AE8B2E5D    NULL
1E7DDA4D-C119-4E47-8478-277952024FD1    NULL

我希望这些 null 为 false。

Answer 1

您可以使用 coalesce() 或 isnull() 来替换 null 的值:

select a.AgentId,
       case coalesce((select acs.IsConnected
            from rmm.tblAgentConnectionStatus acs
            where acs.AgentName = a.AgentName),0)
        when 1 then 'True'
        when 0 then 'False'
        end as ConnectionStatus
from Sentilan2.rmm.tblAgent a
order by AgentName asc

或者只是else 'False':

select a.AgentId,
       case (select acs.IsConnected
            from rmm.tblAgentConnectionStatus acs
            where acs.AgentName = a.AgentName)
        when 1 then 'True'
        else 'False'
        end as ConnectionStatus
from Sentilan2.rmm.tblAgent a
order by AgentName asc