I came across a very peculiar problem the other day. I had a Postgres database and one of the tables had an attribute object_changes which was yaml. Now, the data stored in this attribute was of whatever fields getting updated in a transaction.
I had to check when a given field changed to a particular value. Thus if a record had a column kyc_status which had a value of pending and I needed to track when this value got changed to submitted. I decided to convert this yaml to json first, I have described my approach here.

Querying on json is not quite straight forward. After lots of trial and error, I came across a working solution like this:

SELECT "versions".* FROM "versions" WHERE (
              object_changes::jsonb    @> '{"kyc_status": ["pending", "created"]}'
              OR object_changes::jsonb @> '{"kyc_status": ["received", "created"]}'
            AND item_type = 'Investor'
            AND event = 'update'

Here I am casting the object_changes as jsonb explicitely, and then querying on that json if it contained a key kycs_status which was changed to created from pending or from received.

The object looked something like below:

#<PaperTrail::Version:0x000000000d3d6fc8> {
                    :id => 2567881,
             :item_type => "Investor",
               :item_id => x,
                 :event => "update",
             :whodunnit => nil,
            :object => nil,
            :created_at => Fri, 02 Nov 2018 14:24:52 IST +05:30,
    :object_changes => nil,
        :transaction_id => 2567881,
                :object => {
                                 "id" => 23,
                         "created_at" => "2016-08-08T05:22:20.105Z",
                         "kyc_status" => "pending",
                         "updated_at" => "2018-09-13T10:14:07.879Z"
        :object_changes => {
        "kyc_status" => [
            [0] "pending",
            [1] "blocked"