create or replace function hex2chr(pxx) as
  replace(pxx,'%','').from_hex().decode() ;

create or replace function urldecode(url) as (
  WITH RECURSIVE cte AS (
    -- Base case: set xx as the first sequence of %XX encodings if any
    SELECT
        replace(url, '+', ' ') AS decoded,
        regexp_extract(replace(url, '+', ' '), '(%[0-9A-Fa-f]{2})+') AS xx
    UNION ALL
    -- Recursive case: replace the xx encodings with the decoded character(s)
    SELECT
        replace(decoded, xx, xx.hex2chr()) AS decoded,
        regexp_extract(replace(decoded, xx, '  '), '(%[0-9A-Fa-f]{2})+') as xx
    FROM cte
    WHERE xx != ''
  )
  SELECT decoded FROM cte
  WHERE xx = ''
);

SELECT s, url_decode(s), urldecode(s)
FROM unnest( [
  'http%3A%2F%2Ffoo%20bar%2F',
  'google.com/search?q=%60Abdu%27l-Bah%C3%A1',
  '%25%32%35'
    ]) _(s);