Re: json_populate_recordset

Adrian Klaver <adrian.klaver@xxxxxxxxxxx> · Thu, 7 Jun 2018 11:32:33 -0700

On 06/07/2018 09:56 AM, Pavel Stehule wrote:

2018-06-07 18:51 GMT+02:00 Adrian Klaver <adrian.klaver@xxxxxxxxxxx 
<mailto:adrian.klaver@xxxxxxxxxxx>>:

     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@xxxxxxxxxxx <mailto:adrian.klaver@xxxxxxxxxxx>

--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx