jsonb_agg function creates additional json fields

Question

Why is Postgres jsonb_agg function wrapping the output into additional JSON field?

SELECT jsonb_agg(t) AS json_array
FROM (SELECT jsonb_set('[{"f1": "1","f2": null},  2,  null,  3]', '{0,f1}', '"DELETEME"',true)) t

And it returns this:

[{"jsonb_set": [{"f1": "DELETEME", "f2": null}, {"f3": "1", "f4": null}]}]

How to avoid such behaviour? As I need it to return:

[{"f1": "DELETEME", "f2": null}, {"f3": "1", "f4": null}]

Answer 1

You are converting the whole table alias t to json instead of just that one column. Change t to t.jsonb_set. This works:

=# SELECT jsonb_agg(t.jsonb_set) AS json_array
   FROM (SELECT jsonb_set('[{"f1": "1","f2": null},  2,  null,  3]', '{0,f1}', '"DELETEME"',true)) t;
                   json_array
------------------------------------------------
 [[{"f1": "DELETEME", "f2": null}, 2, null, 3]]
(1 row)