SQL Server extract integers from string using regular expression - sql

Question

I have a string (unc file path) that I need to extract some integers that will be embedded in the string in a semi-predictable way.
Example strings:
\\servername\folder1\FTP\folder2\512/862450_FileBundle.zip
--OR-- : \\servername\folder1\FTP\folder2\512\862450_FileBundle.zip
--OR-- : servername/folder1/FTP/folder2/512/862450_FileBundle.zip
The following regular expression regular expression will match on any integer value that is bounded by a forward or backslash: (\/|\\)\d+(\/|\\)
So the REGEX above would match on "\512\", or "\512/", or "/512/" or even "/512\".
I have tried the following SQL and other variations without success:
DECLARE #testString varchar(50) = '\\servername\folder1\FTP\folder2\512/862450_FileBundle.zip'
SELECT PATINDEX('%(\/|\\)\d+(\/|\\)%', #testString)
I'm not terribly familiar with REGEX and SQL so I'm not even sure this is possible.

Answer 1

SQL Server doesn't have as good pattern matching abilities as regular expressions. You can search for the pattern:
[/\\][0-9]%[/\\]
That is, slash followed by a digit followed by any other string followed by a slash. This will match any characters after the first digit, but your examples have nothing of the form /1abc/.
If this is sufficient, then this does the trick:
select v.*,
left(v2.str2, patindex('%[/\\]%', v2.str2) - 1)
from (values ('\\servername\folder1\FTP\folder2\512/862450_FileBundle.zip')) v(str) cross apply
(values (stuff(v.str, 1, patindex('%[/\\][0-9]%[/\\]%', v.str), ''))) v2(str2)

Answer 2

Other than writing a UDF to loop through the characters, the only thing I can think of is brute force approach...
(The User Defined Function might be your least worst option.)
https://dbfiddle.uk/?rdbms=sqlserver_2017&fiddle=face1befe5e7c74f457846fc37eca649
SELECT
*,
SUBSTRING(test.unc_file_path, headMatch.pos+1, headMatch.chars)
FROM
test
OUTER APPLY
(
SELECT
MIN(pos), MIN(chars)
FROM
(
SELECT
PATINDEX('%' + head + body + tail + '%', test.unc_file_path) AS pos, chars
FROM
(
SELECT '\'
UNION ALL SELECT '/'
)
head(head)
CROSS JOIN
(
SELECT 1, '[0-9]'
UNION ALL SELECT 2, '[0-9][0-9]'
UNION ALL SELECT 3, '[0-9][0-9][0-9]'
UNION ALL SELECT 4, '[0-9][0-9][0-9][0-9]'
UNION ALL SELECT 5, '[0-9][0-9][0-9][0-9][0-9]'
)
body(chars, body)
CROSS JOIN
(
SELECT '\'
UNION ALL SELECT '/'
)
tail(tail)
)
match
WHERE
pos > 0
)
headMatch(pos, chars)