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Re: Regular expression question with Postgres - Mailing list pgsql-general

From Mike Christensen
Subject Re: Regular expression question with Postgres
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Msg-id CABs1bs0L5kghZKe8B1tT-v2DB9hUMgYFNy082gjkUfEx1ygBWA@mail.gmail.com
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In response to Re: Regular expression question with Postgres  (David G Johnston <david.g.johnston@gmail.com>)
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Yea seems right.  I was testing the expression on Rubular (Which uses the Ruby parser) and it worked.  I guess Ruby allows this non-standard expression with the missing lower bounds.  Every reference I could find, though, agrees only the upper bound is optional.


On Thu, Jul 24, 2014 at 1:42 PM, David G Johnston <david.g.johnston@gmail.com> wrote:
Mike Christensen-2 wrote
> I'm curious why this query returns 0:
>
> SELECT 'AAA' ~ '^A{,4}$'
>
> Yet, this query returns 1:
>
> SELECT 'AAA' ~ '^A{0,4}$'
>
> Is this a bug with the regular expression engine?

Apparently since "{,#}" is not a valid regexp expression the engine simply
interprets it as a literal and says 'AAA' != 'A{,4}'

http://www.postgresql.org/docs/9.3/interactive/functions-matching.html#FUNCTIONS-POSIX-REGEXP

Table 9-13. Regular Expression Quantifiers

Note the all of the { } expressions have a lower bound (whether explicit or
implied).

David J.




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