redshift regex get multiple matches and expand rows - sql

Question

I'm working on the URL extraction on AWS Redshift. The URL column looks like this:
url item origin
http://B123//ajdsb apple US
http://BYHG//B123 banana UK
http://B325//BF89//BY85 candy CA
The result I want to get is to get the series that starts with B and also expand rows if there are multiple series in a URL.
extracted item origin
B123 apple US
BYHG banana UK
B123 banana UK
B325 candy CA
BF89 candy CA
BY85 candy CA
My current code is:
select REGEXP_SUBSTR(url, '(B[0-9A-Z]{3})') as extracted, item, origin
from data
The regex part works well but I have problems with extracting multiple values and expand them to new rows. I tried to use REGEXP_MATCHES(url, '(B[0-9A-Z]{3})', 'g') but function regexp_matches does not exist on Redshift...

Answer 1

The solution I use is fairly ugly but achieves the desired results. It involves using REGEXP_COUNT to determine the maximum number of matches in a row then joining the resulting table of numbers to a query using REGEXP_SUBSTR.
-- Get a table with the count of matches
-- e.g. if one row has 5 matches this query will return 0, 1, 2, 3, 4, 5
WITH n_table AS (
SELECT
DISTINCT REGEXP_COUNT(url, '(B[0-9A-Z]{3})') AS n
FROM data
)
-- Join the previous table to the data table and use n in the REGEXP_SUBSTR call to get the nth match
SELECT
REGEXP_SUBSTR(url, '(B[0-9A-Z]{3})', 1, n) AS extracted,
item,
origin
FROM data,
n_table
-- Only keep non-null matches
WHERE n > 0
AND REGEXP_COUNT(url, '(B[0-9A-Z]{3})') >= N

Answer 2

IronFarm's answer inspired me, though I wanted to find a solution that didn't require a cross join. Here's what I came up with:
with
-- raw data
src as (
select
1 as id,
'abc def ghi' as stuff
union all
select
2 as id,
'qwe rty' as stuff
),
-- for each id, get a series of indexes for
-- each match in the string
match_idxs as (
select
id,
generate_series(1, regexp_count(stuff, '[a-z]{3}')) as idx
from
src
)
select
src.id,
match_idxs.idx,
regexp_substr(src.stuff, '[a-z]{3}', 1, match_idxs.idx) as stuff_match
from
src
join match_idxs using (id)
order by
id, idx
;
This yields:
id | idx | stuff_match
----+-----+-------------
1 | 1 | abc
1 | 2 | def
1 | 3 | ghi
2 | 1 | qwe
2 | 2 | rty
(5 rows)