What were all the salary values of players in 2012?
select salary from salary where year = 2012
How about in 2010?
select salary from salary where year = 2010
What is the average number of these results?
select avg(salary) from salary where year = 2010
Could please give all the salary values of players in 2010 and 2001?
select salary from salary where year = 2010 union select salary from salary where year = 2001