--select * from courses

--select * from courses c1 join courses c2 on c1.name = c2.name and c1.year = c2.year
--and c1.crn < c2.crn

--select name, year, count(*) as numtimes from courses 
--group by name, year
--having count(*)>1

--select crn, count(*) as enrolled from grades  group by crn 

--select crn, count(*), name from courses natural join grades group by crn, name

--select * from (select crn, count(*) as enrolled from grades group by crn) natural join courses

--WITH enrollment AS
--  (select crn, count(*) as enrolled from grades group by crn),
--  another_table AS
--  (select ......)
--select * from enrollment natural join courses

--create view enrollment as (select crn, count(*) as enrolled from grades group by crn)

--select * from enrollment

--create table patron (cardnum int, pfirst varchar(100), plast varchar(100));

select * from patron

--insert into patron(pfirst, plast) values ('Catie', 'Welsh')

--update patron
--SET pfirst='Phillip'
--where plast='Kirlin'

--delete from patron where cardnum is null