How do I check if a json key exists in Postgres?

json postgresql psycopg2

Teboto · Mar 8, 2015 · Viewed 52k times · Source

Let's say I have a json that looks like this:

some_json = {'key_a': {'nested_key': 'a'},
             'key_b': {'nested_key': 'b'}}

Note that key_a and key_b are optional keys mapped to dictionaries and may or may not exist.

I have a function that checks if an outer key exists in some_json and returns a boolean.

CREATE FUNCTION key_exists(some_json json, outer_key text)
RETURNS boolean AS $$
BEGIN
    RETURN (some_json->outer_key IS NULL);
END;
$$ LANGUAGE plpgsql;

I get the following error:

ProgrammingError: operator does not exist: json -> boolean

Why is outer_key equating to a boolean? What's the proper syntax to perform this check?

Answer

You can also use the '?' operator like that:

SELECT '{"key_a":1}'::jsonb ? 'key_a'

And if you need to query by nested key, use like this:

SELECT '{"key_a": {"nested_key": "a"}}'::jsonb -> 'key_a' ? 'nested_key'

See http://www.postgresql.org/docs/9.5/static/functions-json.html

NOTE: Only for jsonb type.

How do I check if a json key exists in Postgres?

Answer

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