Filtering and calculating over JSONB object - sql

Question

I have a table with JSONB column which holds data like this:
create table car_stats (
id int primary key,
city varchar,
date timestamp,
info varchar
stats jsonb
)
stats example:
[
{
"brand": "AUDI",
"status": "NEW"
},
{
"brand": "BMW",
"status": "PRODUCTION"
},
{
"brand": "BMW",
"status": "NEW"
},
{
"brand": "BMW",
"status": "NEW"
},
{
"brand": "BMW",
"status": "DELIVERED"
}
]
I want to count percentage of new / production / delivered of car's brand grouped by city and month
CITY MONTH BRAND NEW PRODUCTION DELIVERED
LONDON 3 AUDI 100% 0 0
PARIS 2 BMW 50% 25% 25%
I tried the following, but I have no idea how to calculate elements in JSON (e.g. all BMW in status NEW)
with cte as (
select stats ->> 'brand',
stats ->> 'status',
city,
date
from car_stats
group by city
),
grouped as (
select cte.brand,
cte.country,
cte.date,
ARRAY_TO_JSON(ARRAY_AGG(base)) as statistics
from cte
group by cte.brand, cte.city, cte.date
),
stats as (
count % statistics somehow here.. ?
)
)

Answer 1

You can associate each each element in stats with its corresponding city, and then use sum with group by:
with recursive cte(id, c, p, i, d) as (
select c.id, c.city, (c.stats ->> 0)::jsonb, 1, c.stats from car_stats c
union all
select c.id, c.c, (c.d ->> c.i)::jsonb, c.i+1, c.d from cte c where c.i < jsonb_array_length(c.d)
)
select c.c, extract(month from c1.date), c.p -> 'brand', c.p -> 'factory'
round(sum(case when (c.p -> 'status')::text = '"NEW"' then 1 else 0 end)/count(*)::decimal,2),
round(sum(case when (c.p -> 'status')::text = '"PRODUCTION"' then 1 else 0 end)/count(*)::decimal,2),
round(sum(case when (c.p -> 'status')::text = '"DELIVERED"' then 1 else 0 end)/count(*)::decimal,2)
from cte c join car_stats c1 on c.id = c1.id
group by c.c, extract(month from c1.date), c.p -> 'brand', c -> 'factory'
See demo.

Answer 2

First expand brand and status into separate rows using cross join lateral and then use count filter conditional aggregation.
with t as
(
select city, date_trunc('month', "date")::date y_month, brand, status
from car_stats
cross join lateral
(
select j ->> 'brand' brand,
j ->> 'status' status
from jsonb_array_elements(stats) j
) t
)
select city, y_month, brand,
count(*) filter (where status = 'NEW')::numeric/count(*)*100 "NEW",
count(*) filter (where status = 'PRODUCTION')::numeric/count(*)*100 "PRODUCTION",
count(*) filter (where status = 'DELIVERED')::numeric/count(*)*100 "DELIVERED"
from t
group by city, y_month, brand;