What is the difference between `->>` and `->` in Postgres SQL?

-> returns json (or jsonb) and ->> returns text:

with t (jo, ja) as (values
    ('{"a":"b"}'::jsonb,('[1,2]')::jsonb)
)
select
    pg_typeof(jo -> 'a'), pg_typeof(jo ->> 'a'),
    pg_typeof(ja -> 1), pg_typeof(ja ->> 1)
from t
;
 pg_typeof | pg_typeof | pg_typeof | pg_typeof 
-----------+-----------+-----------+-----------
 jsonb     | text      | jsonb     | text

PostgreSQL provides two native operators -> and ->> to help you query JSON data.

The operator -> returns JSON object field as JSON. The operator ->> returns JSON object field as text.

The following query uses operator -> to get all customers in form of JSON:

SELECT
 info -> 'customer' AS customer
FROM
 orders;

customer
--------
"John Doe"
"Lily Bush"
"Josh William"
"Mary Clark"

And the following query uses operator ->> to get all customers in form of text:

SELECT
 info ->> 'customer' AS customer
FROM
 orders;

customer
--------
John Doe
Lily Bush
Josh William
Mary Clark

You can see more details in the link below http://www.postgresqltutorial.com/postgresql-json/