Re: MySQL search query is not executing in Postgres DB

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> The upshot here appears to be that we're kind of schizophrenic about
> what we want. With things like text || anyelement, anyelement ||
> text, and concat(variadic "any") we are basically asserting that we
> want to treat anything that we don't recognize as a string. But then
> we have other functions (like max and length) where we don't want that
> behavior. I suppose that more than anything this is based on a
> perception that || won't be ambiguous (though whether that perception
> is entirely correct is debatable, given the array-related meanings of
> that operator) but there might be more than one possible sense for
> length() or max(). Is there any principled way of distinguishing
> these cases, or even a rule for what we ought to do by hand in future
> cases of this type, or is it totally arbitrary?

I would not claim that the situation around || is principled in any
fashion. Rather, || was identified as being a key pain point for
the removal of implicit-casts-to-text during 8.3 development, and we
agreed we would reduce the pain by adding operators that effectively
reintroduced the implicit casts *for that one operator only*. I felt
that was still a big step forward compared to implicit casts everywhere.
But if we'd been doing this in a green field, I doubt that you'd see
text || anyelement or anyelement || text in there. I would vote against
introducing more such things in future, on the grounds that there would
be no backwards-compatibility argument for it.

As for the concat() function, IMO it's an ugly kluge. But again, it's
not introducing any global behavior that might have side-effects on
the resolution of other function or operator names.

>> regression=# select lpad(42,8);
>> ERROR: failed to find conversion function from integer to text
>> I'm not sure why that's happening, either, but evidently some
>> additional coercion laxity would required.

> This, however, is a trivial problem; make_fn_arguments just didn't get
> the memo that it might now need to look for assignment casts. See
> attached.

Meh. I'm a bit worried about whether that might have unexpected
consequences, too.

regards, tom lane