Assuming I have a database with a posts table:
> select * from posts where id = 1;
id | title | content
----+----------+------------------------------------
1 | My Title | This is the content of my article. I can compute the word count of the content of a given post like so:
> select sum(array_length(regexp_split_to_array(content, '\s+'), 1)) from posts where id = 1;
sum
-----
7