SELECT si.DomainItemPath,
       si.SystemItemId,
       si.ItemName,
       si.ItemTypeId -- 4 = System Item, 5 = Enumeration
FROM [dbo].[SystemItem] si
LEFT JOIN [dbo].[SystemItemMapAssociation] sima
  on si.SystemItemId = sima.SystemItemId
LEFT JOIN (
  SELECT * 
  FROM [dbo].[SystemItemMap]
  WHERE MappingProjectId in ('3C24EBCB-D6BA-E911-80DE-005056B36109') -- Add in Mapping Projects
) sim 
  on si.SystemItemId = sima.SystemItemId
WHERE sima.SystemItemMapId is NULL
 -- AND si.MappedSystemId = 'B485214C-01D3-E911-80DF-005056B36109' -- Add Data Standard Id