postgresqlHow can I write a PostgreSQL query to retrieve JSON data?

A PostgreSQL query to retrieve JSON data can be written using SELECT json_agg(t) to aggregate the data into a single JSON object.

For example:

SELECT json_agg(t)
FROM (
  SELECT id, name
  FROM users
) t;

This will return a JSON object containing all of the users in the table:

[
  {
    "id": 1,
    "name": "John"
  },
  {
    "id": 2,
    "name": "Jane"
  }
]

The code is composed of the following parts:

SELECT json_agg(t) is used to aggregate the data into a single JSON object.
FROM (SELECT id, name FROM users) t is the subquery used to retrieve the data from the users table.
SELECT id, name is the list of columns to be included in the JSON object.

For more information, please refer to the PostgreSQL documentation.