用Select和Null检查

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
select a.AgentId,
       case(select acs.IsConn