PostgreSQL jsonb_extract_path() Function

Summary: in this tutorial, you will learn how to use the PostgreSQL jsonb_extract_path() function to extract a JSON subobject at the specified path.

Introduction to the PostgreSQL jsonb_extract_path() function

The jsonb_extract_path() function allows you to extract a JSON sub-object from a JSONB value at a specified path.

Here's the basic syntax of the jsonb_extract_path() function:

jsonb_extract_path(target jsonb, VARIADIC path_elems text[])

In this syntax:

• target is a JSONB data from which you want to extract data.
• path_elems is a list of paths that you want to locate the elements in the JSONB data for extraction.

Note that the path is not a JSON path. The syntax for the path_elems parameter is as follows:

• 'key': Access a specific key in the JSON object.
• 'array_index': Access an element in a JSON array using its index.

To navigate through the nested objects or array, you can chain these path components together.

Suppose you have the following JSON object:

{
  "employee": {
    "name": "John Doe",
    "age": 22,
    "contacts": [
      {"type": "email", "value": "john.doe@example.com"},
      {"type": "phone", "value": "408-123-456"}
    ]
  }
}

Here are some examples of the path expressions:

• 'employee' returns the entire employee object.
• ['employee', 'name'] returns the name within the employee object, which is "John Doe".
• ['employee', 'contacts', '0', 'value'] returns the value in the first element of the contacts array, which is john.doe@example.com

PostgreSQL jsonb_extract_path() function examples

Let's take some examples of using the jsonb_extract_path() function.

Setting up a sample table

First, create a new table called documents:

CREATE TABLE documents(
   id SERIAL PRIMARY KEY,
   data JSONB
);

Second, insert two rows into the documents table:

INSERT INTO documents(data)
VALUES
  ('{"employee":{"name":"John Doe","age":22,"contacts":[{"type":"email","value":"john.doe@example.com"},{"type":"phone","value":"408-123-456"}]}}'),
  ('{"employee":{"name":"Jane Doe","age":21,"contacts":[{"type":"email","value":"jane.doe@example.com"},{"type":"phone","value":"408-123-789"}]}}');

Basic jsonb_extract_path() function examples

The following example uses the jsonb_extract_path() function to extract the employee object:

SELECT
  jsonb_extract_path(data, 'employee') employee
FROM
  documents;

Output:

employee
-------------------------------------------------------------------------------------------------------------------------------------------
 {"age": 22, "name": "John Doe", "contacts": [{"type": "email", "value": "john.doe@example.com"}, {"type": "phone", "value": "408-123-456"}]}
 {"age": 21, "name": "Jane Doe", "contacts": [{"type": "email", "value": "jane.doe@example.com"}, {"type": "phone", "value": "408-123-789"}]}
(2 rows)

The following example uses the jsonb_extract_path() function to extract the names of employees:

SELECT
  jsonb_extract_path(data, 'employee', 'name') name
FROM
  documents;

Output:

name
------------
 "John Doe"
 "Jane Doe"
(2 rows)

The following example uses the jsonb_extract_path() function to extract the emails of employees:

SELECT
  jsonb_extract_path(
    data, 'employee', 'contacts', '0',
    'value'
  ) email
FROM
  documents;

Output:

email
---------------------
 "john.doe@example.com"
 "jane.doe@example.com"
(2 rows)

Summary

• Use the jsonb_extract_path() function to extract JSON sub-object at the specified path.