postgres + json object to array - arrays

Question

I would like to know if is possible to 'covnert' a json object to a json array to iterate over a mixed set of data.
I have two rows that look like
{Data:{BASE:{B1:0,color:green}}}
{Data:{BASE:[{B1:1,color:red},{B1:0,color:blue}]}}
I would like to extract the B1 val from all this rows, but I am a bit blocked :)
My first try was a json_extract_array, but it fails on the 1st row (not an array).
Then my second try was a json_array_length with a case, but that fails at the 1st row (not array)
Can I handle this situation in any way?
Basically I need to extract all the rows where B1 > 0 in one of the json array (or object) and maybe return the node that contains B1 > 0.

Answer 1

Your main problem is you mix the data types under the json -> 'Data' -> 'BASE' path, which cannot be handled easily. I could come up with a solution, but you should fix your schema, f.ex. to only contain arrays at that path.
with v(j) as (
values (json '{"Data":{"BASE":{"B1":0,"color":"green"}}}'),
('{"Data":{"BASE":[{"B1":1,"color":"red"},{"B1":0,"color":"blue"}]}}')
)
select j, node
from v,
lateral (select j #> '{Data,BASE}') b(b),
lateral (select substring(trim(leading E'\x20\x09\x0A\x0D' from b::text) from 1 for 1)) l(l),
lateral (select case
when l = '{' and (b #>> '{B1}')::numeric > 0 then b
when l = '[' then (select e from json_array_elements(b) e where (e #>> '{B1}')::numeric > 0 limit 1)
else null
end) node(node)
where node is not null
SQLFiddle

Answer 2

To return the rows where at least one object has B1 > 0
select *
from t
where true in (
select (j ->> 'B1')::int > 0
from json_array_elements (json_column -> 'Data' -> 'BASE') s (j)
)

Answer 3

With a little help from the other answers here, I did this:
with v(j) as (
values (json '{"Data":{"BASE":{"B1":0,"color":"green"}}}'),
('{"Data":{"BASE":[{"B1":1,"color":"red"},{"B1":0,"color":"blue"}]}}')
)
select j->'Data'->'BASE'->>'B1' as "B1"
from v
where j->'Data'->'BASE'->>'B1' is not null
union all
select json_array_elements(j->'Data'->'BASE')->>'B1'
from v
where j->'Data'->'BASE'->>'B1' is null
Divided it into two queries, one which just fetches a single value if there is only one, and one that unwraps the array if there are multiple, utilizing that PostgreSQL returns null if you ask for the text of something that is an array. Then, I just unioned the result from the two queries, which resulted in:
------
| B1 |
------
| 0 |
| 1 |
| 0 |