Computers not reported in 30 days in SCCM

select SMS_R_System.ResourceId, SMS_R_System.ResourceType, SMS_R_System.Name, SMS_R_System.SMSUniqueIdentifier, SMS_R_System.ResourceDomainORWorkgroup, SMS_R_System.Client from SMS_R_System where SMS_R_System.Name in (select Name from SMS_R_System where ((DATEDIFF(day, SMS_R_SYSTEM.AgentTime, getdate()) >=30) and AgentName = "SMS_AD_SYSTEM_DISCOVERY_AGENT")) and SMS_R_System.Name in (select Name from SMS_R_System where ((DATEDIFF(day, SMS_R_SYSTEM.AgentTime, getdate()) >=30) and AgentName = "Heartbeat Discovery"))