How to tabulate a JSON to a recordset in PostgreSQL®

- 2 minutes read - 426 words

PostgreSQL® offers two types of data types to handle JSON data, JSON and JSONB, and provides two different ways to tabulate a JSON to a recordset:

  • the json_populate_recordset (jsonb_populate_recordset for JSONB) function using an existing database type
  • the json_to_recordset (jsonb_to_recordset for JSONB) function defining the list of fields

NOTE: To review the differences between JSON and JSONB check out the related article.

NOTE: more info is available in the PostgreSQL JSON functions documentation page

The dataset

The dataset is the following:

{
    "id": 778,
    "shop": "Luigis Pizza",
    "name": "Edward Olson",
    "phoneNumbers":
        ["(935)503-3765x4154","(935)12345"],
    "address": "Unit 9398 Box 2056\nDPO AP 24022",
    "image": null,
    "pizzas": [
        {
            "pizzaName": "Salami",
            "additionalToppings": ["🥓", "🌶️"]
        },
        {
            "pizzaName": "Margherita",
            "additionalToppings": ["🍌", "🌶️", "🍍"]
        }
    ]
}
Check out the description of the fields The following examples use a pizza order dataset with an order having:
  • id: 778
  • shop: “Luigis Pizza”
  • name: “Edward Olson”
  • phoneNumbers:["(935)503-3765x4154","(935)12345"]
  • address: “Unit 9398 Box 2056\nDPO AP 24022”
  • image: null
  • and two pizzas contained in the pizzas item:
[
    {
        "pizzaName": "Salami",
        "additionalToppings": ["🥓", "🌶️"]
    },
    {
        "pizzaName": "Margherita",
        "additionalToppings": ["🍌", "🌶️", "🍍"]
    }
]
If you want to reproduce the examples, check how to recreate the dataset

It can be recreated with the following script:

create table test(id serial, json_data jsonb);

insert into test(json_data) values (
'{
    "id": 778,
    "shop": "Luigis Pizza",
    "name": "Edward Olson",
    "phoneNumbers":
        ["(935)503-3765x4154","(935)12345"],
    "address": "Unit 9398 Box 2056\nDPO AP 24022",
    "image": null,
    "pizzas": [
        {
            "pizzaName": "Salami",
            "additionalToppings": ["🥓", "🌶️"]
        },
        {
            "pizzaName": "Margherita",
            "additionalToppings": ["🍌", "🌶️", "🍍"]
        }
    ]
}');

Tabulate a JSON to a recordset using an existing database type with the json_populate_recordset function

To tabulate a JSON document to a table record using an existing database type you can use the json_populate_recordset (jsonb_populate_recordset in the example for JSONB column). To tabulate the JSON document:

  • Create a dedicated database type
create type pizza as ("pizzaName" text, "additionalToppings" text[]);
  • Tabulate the JSON using the dedicated function
select p.* from test
cross join lateral 
    jsonb_populate_recordset(
        null::pizza, json_data -> 'pizzas') p;

Result

 pizzaName  | additionalToppings
------------+--------------------
 Salami     | {🥓,🌶️}
 Margherita | {🍌,🌶️,🍍}

Tabulate a JSON to a recordset defining the list of fields with the json_to_recordset function

To tabulate a JSON document to a table recordset defining the list of fields you can use the json_to_recordset (jsonb_to_recordset in the example for JSONB column). To tabulate the JSON document:

select p.* from test
cross join lateral 
    jsonb_to_recordset(json_data -> 'pizzas') 
    as p("pizzaName" text, "additionalToppings" text[]);

Result

 pizzaName  | additionalToppings
------------+--------------------
 Salami     | {🥓,🌶️}
 Margherita | {🍌,🌶️,🍍}

Review all the JSON PostgreSQL use-cases listed in the main page