Calculating Averages (Part 1)

You can calculate average values with the AVG function as shown below. The second statement double checks the answer:

SQL> select avg(num_rows)

  2  from dba_tables

  3  where num_rows is not null

  4  /

AVG(NUM_ROWS)

-------------

   153051.912

SQL> select sum(num_rows) / count(*)

  2  from dba_tables

  3  where num_rows is not null

  4  /

SUM(NUM_ROWS)/COUNT(*)

----------------------

            153051.912

SQL>

Footnote: Since writing this post I have noticed that it is slightly misleading.
Go to part 2 for details.