question Re: Why does Impala 2.0 regex .*? behavior differ from a typical implementation in Support Questions

Why does Impala 2.0 regex .*? behavior differ from a typical implementation

cjard — Thu, 24 Mar 2022 08:20:11 GMT

From the docs at https://docs.cloudera.com/documentation/enterprise/6/6.3/topics/impala_string_functions.html#string_functions__regexp_extract

"This example shows how a pattern string starting with .*? matches the shortest possible portion of the source string, returning the rightmost set of lowercase letters."

select regexp_extract('AbcdBCdefGHI','.*?([[:lower:]]+)',1);

returns def

Every other Regex impl I've worked with would return bcd

I can't make sense of the docs either - "shortest possible string.. returns the rightmost.." - the shortest possible string in a "search from the left" operation returns the leftmost, not the rightmost

Re: Why does Impala 2.0 regex .*? behavior differ from a typical implementation

araujo — Thu, 24 Mar 2022 09:06:55 GMT

@cjard ,

I believe this is a bug. Check this out: https://issues.apache.org/jira/browse/IMPALA-2917

I agree that the documentation needs to be fixed as well.

André

Re: Why does Impala 2.0 regex .*? behavior differ from a typical implementation

cjervis — Thu, 24 Mar 2022 17:01:38 GMT

I've advised the documentation team of the confusing wording for you. Thank you for letting us know.

Re: Why does Impala 2.0 regex .*? behavior differ from a typical implementation

cjard — Thu, 24 Mar 2022 18:33:56 GMT

Thanks all!

I'm curious - does it mean that the documentation will be heavily rewritten to detail how .*? implementation is atypical, or will the bug be fixed so the documentation can be tweaked to be correct?

Re: Why does Impala 2.0 regex .*? behavior differ from a typical implementation

cjervis — Thu, 24 Mar 2022 18:34:03 GMT

That will be up to the documentation team. I alerted them to your concerns so they can look into it.

Re: Why does Impala 2.0 regex .*? behavior differ from a typical implementation

cjard — Thu, 24 Mar 2022 18:35:59 GMT

Fingers crossed it can push the reported bug up the review list a bit then! 🙂 Thanks for the excellent help and attention..