I am practising writing relational algebra (RA) expressions in RA interpreter from Duke, but I can't figure out how to represent group by or having (from SQL). I have this expression, but I need to group it by countries, and get only those that have count>5 (I can work around count with another query, but I don't know how to group):
\project_{country, count(*)}(locationTable);
Also, is there order by in RA?
