Re: Does Type Have = Operator?

Em terça-feira, 10 de maio de 2016, David E. Wheeler <david(at)justatheory(dot)com>
escreveu:

> Hackers,
>
> pgTAP has a function that compares two values of a given type, which it
> uses for comparing column defaults. It looks like this:
>
> CREATE OR REPLACE FUNCTION _def_is( TEXT, TEXT, anyelement, TEXT )
> RETURNS TEXT AS $$
> DECLARE
> thing text;
> BEGIN
> IF $1 ~ '^[^'']+[(]' THEN
> -- It's a functional default.
> RETURN is( $1, $3, $4 );
> END IF;
>
> EXECUTE 'SELECT is('
> || COALESCE($1, 'NULL' || '::' || $2) || '::' || $2 || ',
> '
> || COALESCE(quote_literal($3), 'NULL') || '::' || $2 ||
> ', '
> || COALESCE(quote_literal($4), 'NULL')
> || ')' INTO thing;
> RETURN thing;
> END;
> $$ LANGUAGE plpgsql;
>
> The is() function does an IS DISTINCT FROM to compare the two values
> passed to it. This has been working pretty well for years, but one place it
> doesn’t work is with JSON values. I get:
>
> LINE 1: SELECT NOT $1 IS DISTINCT FROM $2
> ^
> HINT: No operator matches the given name and argument type(s). You
> might need to add explicit type casts.
> QUERY: SELECT NOT $1 IS DISTINCT FROM $2
>
> 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.
>
>
Searching for the operator in pg_operator catalog isn't enought?

Regards,

--
Fabrízio de Royes Mello
Consultoria/Coaching PostgreSQL
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