PostgreSQL JSON building an array without null values - arrays

Question

The following query
SELECT jsonb_build_array(jsonb_build_object('use', 'Home'),
CASE WHEN 1 = 2 THEN jsonb_build_object('use', 'Work')
END)
produces
[{"use":"Home"},null]
When I actually want
[{"use":"Home"}]
How do I go about doing this? json_strip_nulls() does not work for me.

Answer 1

By using a PostgreSQL array like that:
SELECT array_to_json(array_remove(ARRAY[jsonb_build_object('use', 'Home'),
CASE WHEN 1 = 2 THEN jsonb_build_object('use', 'Work') END], null))
which does produce:
[{"use": "Home"}]
while, to be sure:
SELECT array_to_json(array_remove(ARRAY[jsonb_build_object('use', 'Home'),
CASE WHEN 1 = 2 THEN jsonb_build_object('use', 'Work') END,
jsonb_build_object('real_use', 'NotHome')], null))
does produce:
[{"use": "Home"},{"real_use": "NotHome"}]

Answer 2

Creating a custom function seems to be the simplest way.
create or replace function jsonb_build_array_without_nulls(variadic anyarray)
returns jsonb language sql immutable as $$
select jsonb_agg(elem)
from unnest($1) as elem
where elem is not null
$$;
select
jsonb_build_array_without_nulls(
jsonb_build_object('use', 'home'),
case when 1 = 2 then jsonb_build_object('use', 'work') end
)
jsonb_build_array_without_nulls
---------------------------------
[{"use": "home"}]
(1 row)

Answer 3

I'm assuming this query is generaetd dynamically, somehow. If you're in control of the SQL generation, you can also use ARRAY_AGG(...) FILTER(...) instead, which, depending on your real world query, might be more convenient than using all the different array conversion functions suggested by Patrick.
SELECT (
SELECT json_agg(v) FILTER (WHERE v IS NOT NULL)
FROM (
VALUES
(jsonb_build_object('use', 'Home')),
(CASE WHEN 1 = 2 THEN jsonb_build_object('use', 'Work') END)
) t (v)
)
Or also:
SELECT (
SELECT json_agg(v)
FROM (
VALUES
(jsonb_build_object('use', 'Home')),
(CASE WHEN 1 = 2 THEN jsonb_build_object('use', 'Work') END)
) t (v)
WHERE v IS NOT NULL
)

Answer 4

One other way that this can be handled is the following:
SELECT jsonb_build_array(
jsonb_build_object('use', 'Home'),
CASE
WHEN 1 = 2 THEN jsonb_build_object('use', 'Work')
ELSE '"null"'
END
) - 'null'
(Unfortunately it's not really possible to do much with null by itself in postgres -- or most other DBs)
In the case above, '"null"' could be replaced with just about any unique string that would not be mistaken for live data in the array. I would not use numbers since - 0 would actually try to remove the first item from the array, rather than a number within the array. But you could probably use '"0"' and remove using something like - '0' if you wanted.
For those not using CASE, a COALESCE could be used to convert nulls into the desired string (alas, no NVL, IFNULL or ISNULL in postgres, but at least COALESCE is portable)