On 06/19/2011 05:02 PM, Florian Pflug wrote:
On Jun19, 2011, at 22:10 , Tom Lane wrote:
Andrew Dunstan<and...@dunslane.net> writes:
On 06/19/2011 02:56 PM, Robert Haas wrote:
On Sun, Jun 19, 2011 at 9:53 AM, Florian Pflug<f...@phlo.org> wrote:
Amidst the discussion, Alvaro suggested that we resolve the issue
by adding a distinct type for patterns as opposed to text. That'd
allow us to make "~" it's own commutator by defining both
text ~ pattern
and
pattern ~ text.
That's kind of a neat idea. There might be an efficiency benefit to
having a regex type that is precompiled by the input function.
What do we do when we get text or unknown in place of pattern? How are
we going to know if the pattern is supposed to be the left or right operand?
Yeah, this would result in
SELECT 'something' ~ 'something';
failing outright. I don't think it's a good substitute for biting
the bullet and choosing distinct operator names.
Yeah, well, the complaint (put forward mainly by Alvaro) that lead to
this approach in the first place was precisely that
'something' ~ 'anything'
*doesn't* give any indication of what constitutes the pattern and
what the text.
So I consider that to be a feature, not a bug.
BTW, arithmetical operators currently show exactly the same behaviour
postgres# select '1' + '1'
ERROR: operator is not unique: unknown + unknown at character 12
The only argument against that I can see is that it poses
a compatibility problem if "~" remains the pattern matching
operator. I do believe, however, that the chance of
unknown ~ unknown
appearing in actual applications is rather small - that'd only
happen if people used postgresql's regexp engine together with
purely external data.
People can store regular expressions in text fields now, and do, let me
assure you. So the chances you'll encounter text ~ unknown or unknown ~
text or text ~ text are 100%
cheers
andrew
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