Snippet to select last n words from a text in Postgres, which also works for version < 14 without negative indexing.

gistfile1.sql

-- Create table and add a row
create table test_table (
	some_text text
);
insert into test_table(some_text) values (
	'this is a test'
);

-- Last word:
select 
	substring(some_text FROM '((\S+\s+){0,0}\S+$)') as last_word
from test_table 

-- Last two words:
select 
	substring(some_text FROM '((\S+\s+){0,1}\S+$)') as last_two_words
from test_table 

-- Last three words:
select 
	substring(some_text FROM '((\S+\s+){0,2}\S+$)') as last_three_words
from test_table 

-- and so on.

-- First n words can be done via double `reverse`.