select "sid", "name",
extract(year from current_date) - extract(year from "birth_date")
- case when (extract(month from current_date) < extract(month from "birth_date")
             OR extract(month from current_date) <= extract(month from "birth_date")
             AND extract(day from current_date) < extract(day from "birth_date"))
  then 1 else 0 end
as "age",
"cid" from Students