Re: Regex match not back-referencing in function

On Feb 12, 2012, at 13:26, Thom Brown <thom@linux.com> wrote:

> Hi,
>
> Could someone explain the following behaviour?
>
> SELECT regexp_replace(E'Hello & goodbye ',E'([&])','&#' ||
> ascii(E'\\1') || E';\\1');
>
> This returns:
>
>     regexp_replace
> ------------------------
> Hello \& goodbye
> (1 row)
>
> So it matched:
>
> SELECT chr(92);
> chr
> -----
> \
> (1 row)
>
> But notice that when I append the value it's supposed to have matched
> to the end of the replacement value, it shows it should be '&'.
>
> Just to confirm:
>
> SELECT ascii('&');
> ascii
> -------
>    38
> (1 row)
>
> So I'd expect the output of the original statement to be:
>
>     regexp_replace
> ------------------------
> Hello && goodbye
> (1 row)
>
> What am I missing?
>
> --
> Thom
>

The "ASCII" function call is evaluated independently of, and before, the regexp_replace function call and so the E'\\1'
hasno special meaning.  It only has special meaning inside of the regexp_replace function. 

Try just evaluating ascii(E'\\1') by itself and confirm you get "92".

David J.