aggregating json fields

Question

I have a table that holds JSON data. In a query with a GROUP BY clause, I'd like to get an array of all of the JSON field names in the result set.

I tried a query like this:

SELECT array_agg(jsonb_object_keys(data)) 
FROM table 
GROUP BY some_id 
WHERE some_id = 3

For an input data like

some_id | data
--------|---------------
3       | {"foo": "bar"}
4       | {"baz": 3}
3       | {"bar": 4}

I'd like to receive:

array_agg
--------------
{'foo', 'bar'}

But it returns an error: ERROR: set-valued function called in context that cannot accept a set

It seems like I need to somehow convert setof text, which is what jsonb_object_keys returns, into array but I don't know how.

Answer 1

The error message is telling you that you can't use a set returning in the SELECT list. You need to put it into the FROM clause:

SELECT array_agg(t.k) 
FROM table tbl, jsonb_object_keys(tbl.data) as t(k) 
WHERE tbl.some_id = 3
GROUP BY tbl.some_id;