json operators and functions in postgres



~2 min read


378 words

I wrote in the past about Array Intersections in Postgres, which alluded to operators and functions available for arrays within Postgres.

Today, I came across a Postgres function dealing with JSON and found a whole suite of new syntax to learn.

It’s actually pretty cool!

Here’s an example function.

create or replace function generate_log(
    target_op text,
    newj jsonb,
    oldj jsonb
) returns audit_log as $body$
    audit_row audit_log;
    dkey text;

    audit_row = row (
      # …

    if (target_op =DELETE) then
        audit_row.root_resource_name = oldj ->> root_resource_name;
        audit_row.root_resource_id = oldj ->> root_resource_id;
        audit_row.resource_id = oldj ->> resource_id;
        audit_row.from_data = jsonb_strip_nulls(oldj);
      # ...
    end if;
    # ...
    return audit_row;

$body$ language plpgsql;

The gist of the function is that it takes in an operation type (e.g., DELETE) and two json objects and returns the delta between them.

Before we get there, however, we define a few of the return values based on the old JSON’s keys. That is, our new row will have the root_resource_name value that was the root_resource_name of the oldj JSON. That’s what the ->> operator does.

For space considerations, we also remove any null keys using the jsonb_strip_nulls method of Postgres.

There are several standard operators for json and jsonb. From the Postgres Documentation: 1

operator Right Operand Type Return Type Description Example Example Result
-> int json or jsonb Get JSON array element (indexed from zero, negative integers count from the end) ’[{“a”:“foo”},{“b”:“bar”},{“c”:“baz”}]‘::json->2 { “c”:“baz”}
-> text json or jsonb Get JSON object field by key ’{“a”: {“b”:“foo”}}‘::json->‘a’ {“b”:“foo”}
->> int text Get JSON array element as text ‘[1,2,3]‘::json->>2 3
->> text text Get JSON object field as text ’{“a”:1,“b”:2}‘::json->>‘b’ 2
#> text[] json or jsonb Get JSON object at the specified path ’{“a”: {“b”:{“c”: “foo”}}}‘::json#>‘{a,b}’ {“c”: “foo”}
#>> text[] text Get JSON object at the specified path as text ’{“a”:[1,2,3],“b”:[4,5,6]}‘::json#>>‘{a,2}’ 3


  • 1 There are additional operators specifically for jsonb operators that are worth knowing as well.

Hi there and thanks for reading! My name's Stephen. I live in Chicago with my wife, Kate, and dog, Finn. Want more? See about and get in touch!