Seems like an interesting idea, but could use a better example, at least for those who aren't yet intermediate level in SQL.

In what world is this

  WITH countries (code, name) AS (
     ...>   SELECT \* FROM (VALUES
     ...>     ('us', 'United States'), ('fr', 'France'), ('in', 'India')
     ...>   ) AS codes
     ...> )
     ...> SELECT data.code, name FROM data LEFT JOIN countries ON countries.code = data.code;

easier to read than this

  SELECT code,
     ...> CASE code 
     ...>   WHEN 'us' THEN 'United States'
     ...>   WHEN 'fr' THEN 'France'
     ...>   WHEN 'in' THEN 'India'
     ...>  END AS country
     ...> FROM data;