Postgresql json querying in 9.3+ on nested payloads - json

Question

Using postgresql 9.3 (and the new json awesomness) if I have a simple table named 'races' with a two column description such as:
race-id integer,
race-data json
And the json is a payload for each race is something like
{ "race-time": some-date,
"runners": [ { "name": "fred","age": 30, "position": 1 },
{ "name": "john","age": 29, "position": 3 },
{ "name": "sam","age": 31, "position": 2 } ],
"prize-money": 200 }
How can I query the table for:
1) Races where sam has come 1st
2) Races where sam has come 1st and john has come 2nd
3) Where the number of runners with age greater than 30 is > 5 and prize-money > 5000
My experimentation (particularly in querying a nested array payload) so far has lead to further normalizing the data, i.e. creating a table called runners just to make such queries. Ideally I'd like to use this new fangled json query awesomeness but I can't seem to make heads or tails of it in respective to the 3 simple queries.

Answer 1

You can unwind json into one record and then do your queries as you want (see json functions):
with cte as (
select
race_id,
json_array_elements(r.race_data->'runners') as d,
(r.race_data->>'prize-money')::int as price_money
from races as r
), cte2 as (
select
race_id, price_money,
max(case when (d->>'position')::int = 1 then d->>'name' end) as name1,
max(case when (d->>'position')::int = 2 then d->>'name' end) as name2,
max(case when (d->>'position')::int = 3 then d->>'name' end) as name3
from cte
group by race_id, price_money
)
select *
from cte2
where name1 = 'sam' and name2 = 'john'
sql fiddle demo
It's a bit complicated because of your JSON structure. I think that if you change your structure a bit, your queries could be much simplier:
{
"race-time": some-date,
"runners":
{
"1": {"name": "fred","age": 30},
"2": {"name": "sam","age": 31},
"3": {"name": "john","age": 29}
},
"prize-money": 200
}
you can use ->> and -> operators or json_extract_path_text function to get data you need and then use it in the where clause:
select *
from races as r
where
r.race_data->'runners'->'1'->>'name' = 'sam';
select *
from races as r
where
json_extract_path_text(r.race_data, 'runners','1','name') = 'sam' and
json_extract_path_text(r.race_data, 'runners','2','name') = 'john';
select *
from races as r
where
(r.race_data->>'prize-money')::int > 100 and
(
select count(*)
from json_each(r.race_data->'runners')
where (value->>'age')::int >= 30
) >= 2
sql fiddle demo