How to get only the jsonb of specific keys from postgres?

Question

I\'m aware that you can remove keys from a jsonb in postgres using something like this

select \'{\"a\": 1, \"b\": 2, \"c\":3}\'::jsonb -\'a\';
 ?column?
--------         


        

Answer 1

If you want to filter multiple rows with JSONB documents in each of them:

-- Let's generate rows with JSONB column:
WITH s AS (SELECT generate_series(1, 100) num),
g AS (SELECT num, jsonb_build_object('a', s.num, 'b', s.num * 2) obj FROM s),

-- A "filter" adding (in my example only keys of "filter" document remain in result rows)
j AS (SELECT '{"a": "int", "c": "string"}'::jsonb AS filter),
a AS (SELECT (ARRAY(SELECT jsonb_object_keys(filter))) AS ar FROM j),

-- Useless keys removing
o AS (SELECT jsonb_object_agg(l.key, l.value) obj
        FROM g, LATERAL jsonb_each(g.obj) l, a 
        WHERE l.key = ANY(a.ar)
        GROUP BY num)

SELECT * FROM o ORDER BY obj->'a';

Answer 2

You can get just the value like so:

 select '{"a": 1, "b": 2}'::jsonb-> 'a';

If you must, you can transform that back into jsonb manually, or perhaps go through an array, hstore or other intermediate type. Here's the "manual" way

 select ('{ "a": '||('{"a": 1, "b": 2}'::jsonb->'a')::text||'}')::jsonb

Answer 3

You can do this

SELECT jsonb_column->>'key_name_here' as 'column_name_of_your_own' from table_name

In the case of the query asked above, it would be

select '{"a": 1, "b": 2, "c":3}'::jsonb->>'a'

Answer 4

You can filter down to a single key fairly easily like so:

jsonb_object(ARRAY[key, jsonb_data -> key])

...or you can filter down to multiple keys:

(SELECT jsonb_object_agg(key, value) FROM jsonb_each(jsonb_data) WHERE key IN ('a', 'b'))

Or on a more complex condition, if you want:

(
  SELECT jsonb_object_agg(key, value)
  FROM jsonb_each(jsonb_data)
  WHERE
    key NOT LIKE '__%'
    AND jsonb_typeof(value) != 'null'
)

These kinds of questions can be answered very easily by simply reading the documentation.

Answer 5

I actually found that this way works to.

select jsonb_build_object('key', column->'key') from table;

reference: https://www.reddit.com/r/PostgreSQL/comments/73auce/new_user_to_postgres_can_i_grab_multiple_keys_of/