Re: Does Type Have = Operator?

On Tuesday, May 10, 2016, David E. Wheeler <david(at)justatheory(dot)com> wrote:

>
> This makes sense, of course, and I could fix it by comparing text values
> instead of json values when the values are JSON. But of course the lack of
> a = operator is not limited to JSON. So I’m wondering if there’s an
> interface at the SQL level to tell me whether a type has an = operator?
> That way I could always use text values in those situations.
>
>
http://www.postgresql.org/docs/9.5/interactive/catalog-pg-amop.html
http://www.postgresql.org/docs/9.5/interactive/xindex.html

Brute force: you'd have to query pg_amop and note the absence of a row with
a btree (maybe hash too...) family strategy 3 (1 for hash)
[equality] where the left and right types are the same and match the type
in question.

There is likely more to it - though absence is pretty much a given I'd be
concerned about false negatives due to ignoring other factors like
"amoppurpose".

In theory you should be able to trade off convenience for correctness by
calling:

to_regoperator('=(type,type)')

But I've never tried it and it assumes that = is the equality operator and
that its presence is sufficient. I'm also guessing on the text type name
syntax.

http://www.postgresql.org/docs/9.5/interactive/functions-info.html

This option is a young one from what I remember.

David J.