var ans = from a in vw_DimLabAsset
          join w in vw_FactWorker on a.LabAssetAssignedToWorkerKey equals w.WorkerKey
          join o in vw_DimOrganizationHierarchy on w.OrganizationHierarchyKey equals o.OrganizationHierarchyKey
          where o.OrganizationHierarchyUnitLevelThreeNm != null && o.OrganizationHierarchyUnitLevelFourNm != null
          group new { o, a } by new { o.OrganizationHierarchyUnitLevelThreeNm, o.OrganizationHierarchyUnitLevelFourNm, a.LabAssetSerialNbr } into oag
          select new {
              oag.Key.OrganizationHierarchyUnitLevelThreeNm,
              oag.Key.OrganizationHierarchyUnitLevelFourNm,
              oag.Key.LabAssetSerialNbr,
              MinCreated = oag.Min(oa => oa.a.SystemCreatedOnDtm)
          };