Summary: in this tutorial, you will learn how to use the PostgreSQL jsonb_object_keys() function to extract the keys from a JSON object.

Introduction to the PostgreSQL jsonb_object_keys() function

The jsonb_object_keys() function allows you to extract the keys of a JSON object into a set of text values.

Here’s the basic syntax of the jsonb_object_keys() function:

jsonb_object_keys(json_object)

In this syntax:

  • json_object is the JSON object of type JSONB that you want to extract the keys.

The jsonb_object_keys() function returns a set of text values representing the keys in the json_object.

If the json_object is not a JSON object, the jsonb_object_keys() function will issue an error.

If the json_object is NULL, the function will return an empty set.

PostgreSQL jsonb_object_keys() function examples

Let’s take some examples of using the jsonb_object_keys() function.

1) Basic the jsonb_object_keys() function examples

The following example uses the jsonb_object_keys() function to extract the keys of a JSON object as a set of text values:

SELECT
  jsonb_object_keys(
    '{"name": "Joe", "age": 18, "city": "New York"}'
  );

Output:

jsonb_object_keys
-------------------
 age
 city
 name
(3 rows)

2) Using the PostgreSQL jsonb_object_keys() function with table data

First, create a table called person:

CREATE TABLE person (
    id SERIAL PRIMARY KEY,
    info JSONB
);

In the person table, the info column has the type JSONB that stores various information about each person.

Second, insert rows into the person table:

INSERT INTO person (info)
VALUES
    ('{"name": "John", "age": 30, "city": "New York"}'),
    ('{"name": "Alice", "city": "Los Angeles"}'),
    ('{"name": "Bob", "age": 35 }');

Third, get the keys of the objects in the info column:

SELECT jsonb_object_keys(info)
FROM person;

Output:

jsonb_object_keys
-------------------
 age
 city
 name
 city
 name
 age
 name
(7 rows)

To get unique keys from all the stored JSON objects in the info column, you can use the DISTINCT operator:

SELECT DISTINCT jsonb_object_keys(info)
FROM person;

Output:

jsonb_object_keys
-------------------
 age
 city
 name
(3 rows)

3) Dynamically accessing keys

The following example shows how to dynamically access values corresponding to each key retrieved using jsonb_object_keys():

SELECT
    id,
    key,
    info->key AS value
FROM
    person,
    jsonb_object_keys(info) AS key;

Output:

id | key  |     value
----+------+---------------
  1 | age  | 30
  1 | city | "New York"
  1 | name | "John"
  2 | city | "Los Angeles"
  2 | name | "Alice"
  3 | age  | 35
  3 | name | "Bob"
(7 rows)

In this example, the query returns each key along with its corresponding value from the info column of the person table.

Summary

  • Use the jsonb_object_keys() function to extract the keys from a JSON object.