How to query JSON column for unique object values in PostgreSQL - sql

Question

I'm looking to query a table for a distinct list of values in a given JSON column.
In the code snippet below, the Survey_Results table has 3 columns:
Name, Email, and Payload. Payload is the JSON object to I want to query.
Table Name: Survey_Results
Name Email Payload
Ying SmartStuff#gmail.com [
{"fieldName":"Product Name", "Value":"Calculator"},
{"fieldName":"Product Price", "Value":"$54.99"}
]
Kendrick MrTexas#gmail.com [
{"fieldName":"Food Name", "Value":"Texas Toast"},
{"fieldName":"Food Taste", "Value":"Delicious"}
]
Andy WhereTheBass#gmail.com [
{"fieldName":"Band Name", "Value":"MetalHeads"}
{"fieldName":"Valid Member", "Value":"TRUE"}
]
I am looking for a unique list of all fieldNames mentioned.
The ideal answer would be query giving me a list containing "Product Name", "Product Price", "Food Name", "Food Taste", "Band Name", and "Valid Member".
Is something like this possible in Postgres?

Answer 1

Use jsonb_array_elements() in a lateral join:
select distinct value->>'fieldName' as field_name
from survey_results
cross join json_array_elements(payload)
field_name
---------------
Product Name
Valid Member
Food Taste
Product Price
Food Name
Band Name
(6 rows)
How to find distinct Food Name values?
select distinct value->>'Value' as food_name
from survey_results
cross join json_array_elements(payload)
where value->>'fieldName' = 'Food Name'
food_name
-------------
Texas Toast
(1 row)
Db<>fiddle.
Important. Note that the json structure is illogical and thus unnecessarily large and complex. Instead of
[
{"fieldName":"Product Name", "Value":"Calculator"},
{"fieldName":"Product Price", "Value":"$54.99"}
]
use
{"Product Name": "Calculator", "Product Price": "$54.99"}
Open this db<>fiddle to see that proper json structure implies simpler and faster queries.