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Comments - REGEXP_SUBSTR

9 years, 6 months ago Len Nader
Capture Groups

Thrilled that MariaDB supports PCRE, one of the best engines out there.
It seems to me that the REGEXP_SUBSTR function is missing an optional parameter. It would be more useful as
REGEXP_SUBSTR(subject,pattern,group)
where group is 0 by default.
I realize you can do something like
regexp_replace(subject, pattern, '@1')
but that is not super intuitive.
(The @ is actually a double backslash that I don't know how to render on this comment system.)

 
3 years, 10 months ago Christian Proust
Re: Capture Groups

There is one work-around. You can use \K and (?=) to look-ahead and look-behind your subject.

For example:

WITH log(X) AS (
	VALUES
	-- 'over' does not match because 'cute' does not end with a digit
	('Do you know the droid? It is over-cute <3'),
	('I think it is BB-8.'),
	-- 'BB' does not match because it is preceded by 'not'.
	('No it is not BB-8. It is R2-D2.')
)
-- Search a word preceding by 'is ' and followed by '-\\w*\\d'
SELECT REGEXP_SUBSTR(X, 'is \\K\\w+(?=-\\w*\\d)')
FROM log;
-> ''
-> 'BB'
-> 'R2'
 
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