What is the role of the JSON_AGG function?

The JSON_AGG function is a function in the SQL programming language that is used to aggregate data into a single JSON object or array. The function aggregates values from multiple rows and concatenates them into a single JSON object or array. This function is commonly used in database applications that require JSON data to be returned from the database.

The function is available in many SQL database management systems, including PostgreSQL, MySQL, and Oracle. The function takes an expression as its input, which can be a column or a computed value, and returns a single JSON object or array that contains all the aggregated data.

The JSON_AGG function is useful for developers who need to return JSON data from the database. It can be used to create complex JSON objects or arrays that contain data from multiple tables. The function can also be used in conjunction with other SQL functions to produce more complex results.

The JSON_AGG function is a SQL aggregate function that returns a JSON document composed of aggregated values from each input parameter. The input parameters can be a column reference or an expression. Each input parameter results in a name/value pair in the returned JSON document.

For example, the following query uses the JSON_AGG function to aggregate the name and age columns of the users table and return a JSON document with the aggregated values:

SELECT JSON_AGG(
  json_build_object('name', name, 'age', age)
) AS users
FROM users;

The result of this query is a JSON document that looks like this:

[
  {
    "name": "John Doe",
    "age": 30
  },
  {
    "name": "Jane Doe",
    "age": 25
  }
]

The JSON_AGG function can be used to aggregate any type of data, including text, numbers, dates, and boolean values. It is a powerful tool for working with JSON data in SQL.