On 06/07/2018 09:56 AM, Pavel Stehule wrote:
>
>
> 2018-06-07 18:51 GMT+02:00 Adrian Klaver <adrian.klaver@aklaver.com
> <mailto:adrian.klaver@aklaver.com>>:
>
> From here:
>
> https://www.postgresql.org/docs/10/static/functions-json.html
> <https://www.postgresql.org/docs/10/static/functions-json.html>
>
> select * from json_populate_record(null::myrowtype, '{"a": 1, "b":
> ["2", "a b"], "c": {"d": 4, "e": "a b c"}}')
>
> What is the null::myrowtype doing?
>
>
> this function uses polymorphic parameters - its some like
>
> create or replace function fx(in anyelement, json) returns anyelement ..
>
> output polymorphic value requires minimally one input polymorphic value
> for type specification. Postgres has not possibility to pass only
> datatype - so pattern null:type is used instead.
Alright, so it is bootstrapping a polymorphic type off null. Thanks.
>
> Regards
>
> Pavel
>
>
>
> Thanks,
> --
> Adrian Klaver
> adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
>
>
--
Adrian Klaver
adrian.klaver@aklaver.com
