Creating JSON Array in PostgreSQL by reading comma separated values

Question

I have 2 tables in my PostgreSQL database.

Table 1 has the Product_Details :

Product_Name	Allowed_Transaction_Modes	Category
Salary_Account	ATM,NEFT,UPI,GPay	Premium
Savings_Account	ATM,UPI, GPay	Silver

The second table contains the description of these allowed transaction modes - Transaction_Models :

Allowed_Trans_Modes	Description
NEFT	National Electronic Funds Transfer
UPI	Unified Payments Interface
GPay	Google Pay
ATM	Automated teller machine

I need to create the following JSON output by using a select query

[
  {
    "Product Name": "Salary Account",
    "Allowed_Transaction_Modes": [
      {
        "code": "ATM",
        "description": "Automated teller machine"
      },
      {
        "code": "NEFT",
        "description": "National Electronic Funds Transfer"
      },
      {
        "code": "UPI",
        "description": "Unified Payments Interface"
      },
      {
        "code": "GPay",
        "description": "Google Pay"
      }
    ],
    "Category": "Premium"
  },
  {
    "Product Name": "Salary Account",
    "Allowed_Transaction_Modes": [
      {
        "code": "ATM",
        "description": "Automated teller machine"
      },
      {
        "code": "UPI",
        "description": "Unified Payments Interface"
      },
      {
        "code": "GPay",
        "description": "Google Pay"
      }
    ],
    "Category": "Silver"
  }
]

Tried writing a few queries from Google but they do not work.

Answer 1

First, You need to convert the string to an array then join it with Allowed_Trans_Modes . After that, you can use jsonb_agg to create array of JSON

Demo

with data as (
  select
    pd."Product_Name",
    pd."Category",
    jsonb_agg(
      jsonb_build_object(
        'code', 
        tm."Allowed_Trans_Modes", 
        'description',
        tm."Description"
      )
    ) as agg
  from
    "Product_Details" pd,
    "Transaction_Modesl" tm
  where
    tm."Allowed_Trans_Modes" = any(string_to_array(pd."Allowed_Transaction_Modes", ','))
  group by
    1, 2)
select
  jsonb_agg(
    jsonb_build_object(
      'Product Name',
      "Product_Name",
      'Allowed_Transaction_Modes',
      agg,
      'Category',
      "Category"
    )
  )
from
  data