JSONB nested array query - check existence of attribute - sql

Question

I want to check the existence of an attribute in a JSONB column using SQL.
Using this is I can check if attribute equals value:
SELECT count(*) AS "count" FROM "table" WHERE column->'node' #> '[{"Attribute":"value"}]'
What syntax do I use to check the existence of Attribute?

Answer 1

Usually you'll check for null:
SELECT count(*) AS "count" FROM "table"
WHERE column->'node'->'Attribute' is not null

Answer 2

The ? operator means Does the string exist as a top-level key within the JSON value? However, you want to check whether a key exists in a nested json array of objects, so you cannot use the operator directly. You have to unnest arrays.
Sample data:
create table my_table(id serial primary key, json_column jsonb);
insert into my_table (json_column) values
('{"node": [{"Attribute":"value"}, {"other key": 0}]}'),
('{"node": [{"Attribute":"value", "other key": 0}]}'),
('{"node": [{"Not Attribute":"value"}]}');
Use jsonb_array_elements() in a lateral join to find out whether a key exists in any element of the array:
select
id,
value,
value ? 'Attribute' as key_exists_in_object
from my_table
cross join jsonb_array_elements(json_column->'node')
id | value | key_exists_in_object
----+----------------------------------------+----------------------
1 | {"Attribute": "value"} | t
1 | {"other key": 0} | f
2 | {"Attribute": "value", "other key": 0} | t
3 | {"Not Attribute": "value"} | f
(4 rows)
But this is not exactly what you are expecting. You need to aggregate results for arrays:
select
id,
json_column->'node' as array,
bool_or(value ? 'Attribute') as key_exists_in_array
from my_table
cross join jsonb_array_elements(json_column->'node')
group by id
order by id
id | array | key_exists_in_array
----+--------------------------------------------+---------------------
1 | [{"Attribute": "value"}, {"other key": 0}] | t
2 | [{"Attribute": "value", "other key": 0}] | t
3 | [{"Not Attribute": "value"}] | f
(3 rows)
Well, this looks a bit complex. You can make it easier using the function:
create or replace function key_exists_in_array(key text, arr jsonb)
returns boolean language sql immutable as $$
select bool_or(value ? key)
from jsonb_array_elements(arr)
$$;
select
id,
json_column->'node' as array,
key_exists_in_array('Attribute', json_column->'node')
from my_table
id | array | key_exists_in_array
----+--------------------------------------------+---------------------
1 | [{"Attribute": "value"}, {"other key": 0}] | t
2 | [{"Attribute": "value", "other key": 0}] | t
3 | [{"Not Attribute": "value"}] | f
(3 rows)