On Mon, Dec 29, 2014 at 4:51 PM, Mike Cardwell [via PostgreSQL] <[hidden email]> wrote:
* on the Mon, Dec 29, 2014 at 04:23:22PM -0700, David G Johnston wrote:
>>> WHERE hostname='nißan.com' >>> >> >> _IF_ Postgres had a punycode function, then you could use: >> WHERE punycode(hostname) = punycode('nißan.com') > > If the OP wraps what he is doing up into a function that is what you end up > getting: a memoized punycode function. > > http://en.wikipedia.org/wiki/Memoization > > It has to be defined as volatile but basically write the function to check > for the provided input on the indexed table and if it doesn't exist the > function will calculate the punycode value and store it onto the table > before returning the punycode value to the caller.
I'm not sure all that is necessary. It could be quite a simple function,
like the lower() function. So what I would do is this:
CREATE UNIQUE INDEX hostnames_hostname_key ON hostnames (lower(punycode_encode(hostname)));
That would prevent adding more than one representation for the same hostname to the column.
Except two different hostname can resolve to the same punycode_encode(hostname) value so the unique index won't work.
It was also mentioned that using the Perl encoding function was non-performant; which is why caching the data into a memoization table has value.
WHERE lower(punycode_encode(hostname)) = lower(punycode_encode('any-representation'))
I'm not for knowing the rules of punycode but I'm not seeing what value lower() provides here...
There doesn't need to be any extra table storage for the punycode encoded version.
