Show information for manufacturers that opened on or after 1990.
select * from manufacturer where open_year >= 1990
How about before 1990?
select * from manufacturer where open_year < 1990
What is the maximim number of shops among these manufacturers?
select max(num_of_shops) from manufacturer where open_year < 1990
Also show the average number of factories for this group.
select max(num_of_shops), avg(num_of_factories) from manufacturer where open_year < 1990