Re: DB2 regex bug with look around ?

[Craig Richards <craig@xxxxxxxxxxxxxxxx>]

Yes well spotted sorry I'm not able to cut and paste to this account from
work so I typed it ( badly! ) on my phone

but that's not the issue :-)

If you check the regex and the string it's applied to, and ignore my typos
( sorry ) I think you'll find it doesn't select the correct matched text (
or else my understanding is wrong )

On Thursday, 28 April 2016, Paul Bailey <PaulBailey@xxxxxxxxxx> wrote:

> Just to point out the obvious, you've got a closing bracket missing after
> the "(?!a" in the two examples you posted. I'm assuming it is a typing
> error, but thought I'd better check:
>
> Regexp_substr( 'B2B' , '(?<!a)\d(?!a' )
>
> Regexp_replace( 'B2B' , '(?<!a)\d(?!a', '#' )
>
>
> -Paul.
>
>
> -----Original Message-----
> From: WDSCI-L [mailto:wdsci-l-bounces@xxxxxxxxxxxx <javascript:;>] On
> Behalf Of Craig Richards
> Sent: 28 April 2016 10:42
> To: Rational Developer for IBM i / Websphere Development Studio Client for
> System i & iSeries
> Subject: [WDSCI-L] DB2 regex bug with look around ?
>
> Apologies if this isn't quite the correct forum for this question, but it
> seems a good place to get a chance of a second opinion...
>
> Has anyone noticed anything funny with the look around regex capabilities
> of DB2 ( 7.1 )
>
> For example
>
> Applying
>
> (?<!a)\d(?!a)
>
> To
>
> B2B
>
> It should return
>
> 2
>
> But it seems to find a match but with no text returned.
>
> E.g if you run:
>
> Select
> Regexp_substr( 'B2B' , '(?<!a)\d(?!a' )
> From sysibm/sysdummy1
>
> It doesn't return null and it appears as blank in STRSQL.
>
> whereas if you run the regex over 'a2B' you clearly get null returned.
>
> But it should select the digit as far as I understand.
>
> Further,
>
> Select
> Regexp_replace( 'B2B' , '(?<!a)\d(?!a', '#' ) From sysibm/sysdummy1
>
> Will return B#2B
>
> which seems to indicate that the regex selected the position just after
> the B where the negative look behind matched, but then didn't appear to go
> on and match the digit.
>
> Does this make sense to anyone?
>
> The regex is saying "find me a digit which doesn't have an "a" on either
> side of it"
>
> Am I missing something obvious?
>
> Thanks,
> Craig
> --
> This is the Rational Developer for IBM i / Websphere Development Studio
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