Thank you both. This has been extremely helpful. I still have more work
to do but this has made it possible to start playing with something,
and reading about it when it doesn't work.
On Sun, 2024-09-15 at 10:13 -0700, Willow Chargin wrote:
> On Sun, Sep 15, 2024 at 4:23 AM Alban Hertroys <haramrae@xxxxxxxxx>
> wrote:
> >
> > The drawback is that you have to specify all fields and types, but
> > you don’t need to cast the values all the time either.
>
> Here is a variant of Alban's first method that does not require
> specifying all fields and types, and so works with heterogeneous
> values:
>
> WITH t AS (
> SELECT jsonb($$[
> {"a": 1, "b": -3, "c": 1},
> {"a": 2, "b": -2, "c": 2},
> {"a": 3, "b": -1, "c": 3},
> {"a": 3, "b": -3, "c": 4}
> ]$$) arr
> )
> SELECT
> jsonb_agg(new_element ORDER BY idx) new_arr
> FROM t, LATERAL (
> SELECT idx, jsonb_object_agg(key, CASE
> WHEN key = 'a'
> THEN least(old_value::numeric, 2)::text::jsonb
> WHEN key = 'b'
> THEN greatest(old_value::numeric, -
> 2)::text::jsonb
> ELSE old_value
> END)
> FROM
> jsonb_array_elements(arr)
> WITH ORDINALITY old_elements(old_element, idx),
> jsonb_each(old_element) each(key, old_value)
> GROUP BY idx
> ) new_elements(idx, new_element)
>
> I also took the liberties of using `least` / `greatest` to simplify
> the
> clamping operations, and using `WITH ORDINALITY` / `ORDER BY` on the
> array scan and re-aggregation to make the element ordering explicit
> rather than relying on the query engine to not re-order the rows.
>
> https://www.postgresql.org/docs/16/functions-conditional.html#FUNCTIONS-GREATEST-LEAST
> https://www.postgresql.org/docs/16/queries-table-expressions.html#QUERIES-TABLEFUNCTIONS
I found that I needed to old_value::text::numeric to get Willow's code
to work, but I imagine this is due to the ancientness of the postgresql
I am using.
thanks
Dan
