Re: Regular expression query

> Rodger Donaldson <rodgerd@diaspora.gen.nz> writes:
> > SELECT url 
> > FROM sites
> > WHERE url ~ url || '\\s+'
> 
> > While this concatenation works with the LIKE directive (ie LIKE url || '%'),
> > postgresql barfs on it in a regexp with the error:
> 
> > ERROR:  Unable to identify an operator '||' for types 'bool' and 'unknown'
> >     You will have to retype this query using an explicit cast
> 
> LIKE and ~ do not have the same precedence.  See
> http://www.postgresql.org/docs/postgres/operators.htm.
> ~ and || actually fall in the same category ("all other") and therefore
> are grouped left-to-right; so you're getting (url ~ url) || '...'.
> 
> > The other aspect of this is that it seems that postgresql's regexp engine
> > doesn't understand some expected regexps; I've tried both escaped and
> > unescaped versions of, eg \w, \s, \n and so on a pg seems to ignore them.
> 
> The regexp package we currently use implements POSIX 1003.2 regexps
> (see src/backend/regex/re_format.7).  I believe there is an item on the
> TODO list about upgrading the regexp parser to something more modern
> ... feel free to hop on that project if it's bugging you ...

I bug Henry Spencer regularly.  His new code is in TCL/TK, but has not
been released into any other code.

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