The following tables does not expose the fields

Fields :

1. CreatedOn
2. CreatedBy
3. ModifiedOn
4. ModifiedBy 

Tables :

1. attribute
2. attributeimageconfig    
3. canvasapp          
4. entity            
5. entityimageconfig     
6. entitykey          
7. entityrelationship     
8. optionset          
9. ribboncustomization
10. systemform         

For example, when you make "select * from entity", using Sql4Cds, you cannot obtain these fields