What is the difference between `->>` and `->` in Postgres SQL?
->
returns json(b) 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 customerFROM 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 customerFROM orders;
customer--------John DoeLily BushJosh WilliamMary Clark
You can see more details in the link belowhttp://www.postgresqltutorial.com/postgresql-json/
Postgres offers 2 operators to get a JSON member:
- the arrow operator:
->
returns type JSON or JSONB - the double arrow operator:
->>
returns type text
We must also understand that we now have 2 different kinds of null:
- (null) postgres null type
- null json/b null type
I created an example on jsfiddle
Let's create a simple table with a JSONB field:
create table json_test ( id integer, val JSONB);
and insert some test-data:
INSERT INTO json_test (id, val) values(1, jsonb_build_object('member', null)),(2, jsonb_build_object('member', 12)),(3, null);
Output as we see it in sqlfiddle:
id | val----+----------------- 1 | {"member": null} 2 | {"member": 12} 3 | (null)
Notes:
- contains a JSONB object and the only field
member
is null - contains a JSONB object and the only field
member
has the numeric value12
- is (null): i.e. the whole column is (null) and does not contain a JSONB object at all
To better understand the differences, let's look at the types and null-checks:
SELECT id, val -> 'member' as arrow, pg_typeof(val -> 'member') as arrow_pg_type, val -> 'member' IS NULL as arrow_is_null, val ->> 'member' as dbl_arrow, pg_typeof(val ->> 'member') as dbl_arrow_pg_type, val ->> 'member' IS NULL as dbl_arrow_is_null, CASE WHEN jsonb_typeof(val -> 'member') = 'null' THEN true ELSE false END as is_json_nullfrom json_test;
Output:
+----+--------+---------------+---------------+-----------+-------------------+-------------------+--------------+| id | arrow | arrow_pg_type | arrow_is_null | dbl_arrow | dbl_arrow_pg_type | dbl_arrow_is_null | is_json_null |+----+--------+---------------+---------------+-----------+-------------------+-------------------+--------------+| 1 | null | jsonb | false | (null) | text | true | true |+----+--------+---------------+---------------+-----------+-------------------+-------------------+--------------+| 2 | 12 | jsonb | false | 12 | text | false | false |+----+--------+---------------+---------------+-----------+-------------------+-------------------+--------------+| 3 | (null) | jsonb | true | (null) | text | true | false |+----+--------+---------------+---------------+-----------+-------------------+-------------------+--------------+
Notes:
- for
{"member": null}
:val -> 'member' IS NULL
is falseval ->> 'member' IS NULL
is true
is_json_null
can be used to get only the json-null condition