The aim of this post is not to explain how the APPROX_MEDIAN function works (you find basic information in the documentation) but to show you the results of a test case I run to assess how well it works.
Here’s what I did…
I started in the Oracle Database Public Cloud an instance of version 12.2.
Then I created a table with several numerical columns (the name of each column shows how many distinct values it contains), loaded 150 million rows into it (the size of the segment is 20 GB), and gathered the object statistics.