Show me the name of all stadiums.
select name from stadium
What about their opening years?
select name,opening_year from stadium
Only list those opened after 2006.
select name,opening_year from stadium where opening_year > 2006
Show me the countries which has any of those stadiums.
select country from stadium where opening_year > 2006
What about the countries in file that are not among them.
select country from stadium except select country from stadium where opening_year > 2006