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Postgres jsonb_each() function

Expands JSONB into a record per key-value pair

The jsonb_each function in Postgres is used to expand a JSONB object into a set of key-value pairs.

It is useful when you need to iterate over a JSONB object's keys and values, such as when you're working with dynamic JSONB structures where the schema is not fixed. Another important use case is performing data transformations and analytics.

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Function signature

jsonb_each(json JSON) -> SETOF record(key text, value json)

The function returns a set of rows, each containing a key and the corresponding value for each field in the input JSONB object. The key is of type text, while the value is of type JSONB.

Example usage

Consider a JSONB object representing a user's profile information. The JSONB data will have multiple attributes and might look like this:

{
  "username": "johndoe",
  "age": 30,
  "email": "johndoe@example.com"
}

We can go over all the fields in the profile JSONB object using jsonb_each, and produce a row for each key-value pair.

SELECT key, value
FROM jsonb_each('{"username": "johndoe", "age": 30, "email": "johndoe@example.com"}');

This query returns the following results:

| key      | value                 |
|----------|-----------------------|
| username | "johndoe"             |
| age      | 30                    |
| email    | "johndoe@example.com" |

Advanced examples

Assign custom names to columns output by jsonb_each

You can use AS to specify custom column names for the key and value columns.

SELECT attr_name, attr_value
FROM jsonb_each('{"username": "johndoe", "age": 30, "email": "johndoe@example.com"}')
AS user_data(attr_name, attr_value);

This query returns the following results:

| attr_name | attr_value            |
|-----------|-----------------------|
| username  | "johndoe"             |
| age       | 30                    |
| email     | "johndoe@example.com" |

Use jsonb_each output as a table or row source

Since jsonb_each returns a set of rows, you can use it as a table source in a FROM clause. This lets us join the expanded JSONB data in the output with other tables.

Here, we're joining each row in the user_data table with the output of jsonb_each:

CREATE TABLE user_data (
    id INT,
    profile JSON
);
INSERT INTO user_data (id, profile)
VALUES
    (123, '{"username": "johndoe", "age": 30, "email": "johndoe@example.com"}'),
    (140, '{"username": "mikesmith", "age": 40, "email": "mikesmith@example.com"}');

SELECT id, key, value
FROM user_data, jsonb_each(user_data.profile);

This query returns the following results:

| id  | key      | value                   |
|-----|----------|-------------------------|
| 123 | username | "johndoe"               |
| 123 | age      | 30                      |
| 123 | email    | "johndoe@example.com"   |
| 140 | username | "mikesmith"             |
| 140 | age      | 40                      |
| 140 | email    | "mikesmith@example.com" |

Additional considerations

Performance implications

When working with large JSONB objects, jsonb_each may lead to performance overhead, as it expands each key-value pair into a separate row.

Alternative functions

  • jsonb_each_text - Similar functionality to jsonb_each but returns the value as a text type instead of JSONB.
  • jsonb_object_keys - It returns only the set of keys in the JSONB object, without the values.
  • json_each - It provides the same functionality as jsonb_each, but accepts JSON input instead of JSONB.

Resources

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