It's json_object_agg in PostgreSQL
https://www.postgresql.org/docs/current/static/functions-agg...
https://www.postgresql.org/docs/current/static/functions-agg...
This is how standard SQL JSON_OBJECTAGG works: https://modern-sql.com/blog/2017-06/whats-new-in-sql-2016#js...
It can actually do much more:
<JSON object aggregate constructor> ::= JSON_OBJECTAGG <left paren> <JSON name and value> [ <JSON constructor null clause> ] [ <JSON key uniqueness constraint> ] [ <JSON output clause> ] <right paren>
This free technical report of ISO has some examples: http://standards.iso.org/ittf/PubliclyAvailableStandards/c06...
Is it really that different to not even warrant a note in the table?
Clearly you know better than I do, but the big red X surprised me as the fantastic JSON support is one of the reasons why I tend to reach for Postgres so often over other DB engines.
There is nothing against using non-standard functionality in that case. In this particular case. PostgreSQL got JSON support (~2012?) long before it was added to the standard (2016). Obviously, their JSON functions differ from the standard (as they didn't lobby their functions into the standard).
However, slowly but surely database will add the standard functionality, which makes life easier.
Having that said, the standard JSON_OBJECTAGG is more powerful as it gives you control over null handling (NULL ON NULL -vs- ABSENT ON NULL) and allows checking for duplicate keys ([(WITH|WITHOUT) UNIQUE KEYS]).