Extracting key from the value of json object in postgres

Question

Let us say I have a json object {'key1':0.5,'key2':0.3,'key3':0.1} in a particular column in a table called test. I want to return the key of the highest value. To get the highest value, in postgres, I can write this query:

select greatest(column1->'key1',column1->'key2',column1->'key3') from test

Now, it returns the greatest value. But the one I want is the key associated with the highest value. Is this possible in postgres json querying?

Answer 1

You need to extract all key/value pairs as rows. Once you have done that, it's a greatest-n-per-group problem - without the "group" though as you are looking at all rows.

select k,val
from (
  select t.*, row_number() over (order by t.val::numeric desc) as rn
  from jsonb_each_text('{"key1":0.5,"key2":0.3,"key3":0.1}'::jsonb) as t(k,val)
) t
where rn = 1;

Online example: http://rextester.com/OLBM23414