Aggregate functions: AVG

1. SELECT AVG(released_year)
2. FROM books;
3.  
4. SELECT AVG(pages)
5. FROM books;
6.  
7. SELECT AVG(stock_quantity)
8. FROM books
9. GROUP BY released_year;
10.  
11. SELECT released_year, AVG(stock_quantity)
12. FROM books
13. GROUP BY released_year;
14.  
15. SELECT author_fname, author_lname, AVG(pages) FROM books
16. GROUP BY author_lname, author_fname;