Access deeper elements of a JSON using postgresql 9.4 - json

Question

I want to be able to access deeper elements stored in a json in the field json, stored in a postgresql database. For example, I would like to be able to access the elements that traverse the path states->events->time from the json provided below. Here is the postgreSQL query I'm using:
SELECT
data#>> '{userId}' as user,
data#>> '{region}' as region,
data#>>'{priorTimeSpentInApp}' as priotTimeSpentInApp,
data#>>'{userAttributes, "Total Friends"}' as totalFriends
from game_json
WHERE game_name LIKE 'myNewGame'
LIMIT 1000
and here is an example record from the json field
{
"region": "oh",
"deviceModel": "inHouseDevice",
"states": [
{
"events": [
{
"time": 1430247045.176,
"name": "Session Start",
"value": 0,
"parameters": {
"Balance": "40"
},
"info": ""
},
{
"time": 1430247293.501,
"name": "Mission1",
"value": 1,
"parameters": {
"Result": "Win ",
"Replay": "no",
"Attempt Number": "1"
},
"info": ""
}
]
}
],
"priorTimeSpentInApp": 28989.41467999999,
"country": "CA",
"city": "vancouver",
"isDeveloper": true,
"time": 1430247044.414,
"duration": 411.53,
"timezone": "America/Cleveland",
"priorSessions": 47,
"experiments": [],
"systemVersion": "3.8.1",
"appVersion": "14312",
"userId": "ef617d7ad4c6982e2cb7f6902801eb8a",
"isSession": true,
"firstRun": 1429572011.15,
"priorEvents": 69,
"userAttributes": {
"Total Friends": "0",
"Device Type": "Tablet",
"Social Connection": "None",
"Item Slots Owned": "12",
"Total Levels Played": "0",
"Retention Cohort": "Day 0",
"Player Progression": "0",
"Characters Owned": "1"
},
"deviceId": "ef617d7ad4c6982e2cb7f6902801eb8a"
}
That SQL query works, except that it doesn't give me any return values for totalFriends (e.g. data#>>'{userAttributes, "Total Friends"}' as totalFriends). I assume that part of the problem is that events falls within a square bracket (I don't know what that indicates in the json format) as opposed to a curly brace, but I'm also unable to extract values from the userAttributes key.
I would appreciate it if anyone could help me.
I'm sorry if this question has been asked elsewhere. I'm so new to postgresql and even json that I'm having trouble coming up with the proper terminology to find the answers to this (and related) questions.

Answer 1

You should definitely familiarize yourself with the basics of json
and json functions and operators in Postgres.
In the second source pay attention to the operators -> and ->>.
General rule: use -> to get a json object, ->> to get a json value as text.
Using these operators you can rewrite your query in the way which returns correct value of 'Total Friends':
select
data->>'userId' as user,
data->>'region' as region,
data->>'priorTimeSpentInApp' as priotTimeSpentInApp,
data->'userAttributes'->>'Total Friends' as totalFriends
from game_json
where game_name like 'myNewGame';
Json objects in square brackets are elements of a json array.
Json arrays may have many elements.
The elements are accessed by an index.
Json arrays are indexed from 0 (the first element of an array has an index 0).
Example:
select
data->'states'->0->'events'->1->>'name'
from game_json
where game_name like 'myNewGame';
-- returns "Mission1"

Answer 2

select
data->'states'->0->'events'->1->>'name'
from game_json
where game_name like 'myNewGame';
This did help me