Extract domain and subdomains in Big Query - google-bigquery

Question

I need to extract domains, subdomains and subsubomains from a link.
Example https://stackoverflow.com/users/17141604/badinmaths
domain : https://stackoverflow.com/
subdomain : https://stackoverflow.com/users
subsubdomain : https://stackoverflow.com/users/17141604 (even if the subsubdomain is weird)
https://stackoverflow.com/questions/ask
domain : https://stackoverflow.com/
subdomain : https://stackoverflow.com/questions
Here : no subsubdomain
I already know how to extract domain with NET.HOST but I need to extract other parts.
I have a large number of URL where I have to apply this method.

Answer 1

There might be better way but you can consider below.
WITH sample_table AS (
SELECT 'https://stackoverflow.com/users/17141604/badinmaths' url
UNION ALL
SELECT 'https://stackoverflow.com/questions/ask'
)
SELECT domain,
domain || paths[SAFE_OFFSET(0)] AS subdomain,
domain || paths[SAFE_OFFSET(0)] || '/' || paths[SAFE_OFFSET(1)] AS subsubdomain
FROM sample_table,
UNNEST ([STRUCT(SPLIT(url, NET.HOST(url)) AS split_url)]),
UNNEST ([STRUCT(split_url[SAFE_OFFSET(0)] || NET.HOST(url) || '/' AS domain)]),
UNNEST ([STRUCT(REGEXP_EXTRACT_ALL(split_url[SAFE_OFFSET(1)], r'(\w+)\/') AS paths)]);
Query results
UNNEST ([STRUCT(*expression* AS *field_name*)])
with this trick, you can treat field_name as column_name of base table.
useful to reduce the repetition of same expression in the select list
SPLIT(url, NET.HOST(url)) returns an array of ['https', '/questions/ask'] which will be used later to reconstruct domain and subdomains.
For the regular expression, see here regex101