-- Create new notification_history table and primary key.
CREATE TABLE notification_history_pivot AS SELECT * FROM notification_history WHERE 1=2;
ALTER TABLE notification_history_pivot ADD PRIMARY KEY (id);

-- Update values of notification_status, billable_units, updated_at, sent_by, sent_at based on new updates coming into the notification_history table.
CREATE OR REPLACE FUNCTION update_pivot_table()
RETURNS TRIGGER
LANGUAGE plpgsql AS 
$$
BEGIN
    UPDATE notification_history_pivot SET   notification_status = NEW.notification_status,
                                            billable_units = NEW.billable_units,
                                            updated_at = NEW.updated_at,
                                            sent_by = NEW.sent_by,
                                            sent_at = NEW.sent_at
    WHERE notification_history_pivot.id = NEW.id;

    RETURN NEW;
END
$$;

DROP TRIGGER IF EXISTS update_pivot on notification_history;
CREATE TRIGGER update_pivot AFTER UPDATE OF notification_status, billable_units, updated_at, sent_by, sent_at ON notification_history
FOR EACH ROW
  EXECUTE PROCEDURE update_pivot_table();

Create foreign key constraints in notification_history_pivot with dummy names - prefix with "nh_"

insert data into notification_history_pivot in batches

create remaining indices on notification_history_pivot

-- Run basic sanity checks on data in notification_history_pivot, ensuring same number of entries present in notification_history and notification_history_pivot

ALTER TABLE notification_history RENAME TO notification_history_old;
Drop constraints on notification_history_old
ALTER TABLE notification_history_pivot RENAME TO notification_history;
Create foreign key constraints in notification_history using correct names. Names of constraints will now be available after step above ("Drop constraints on notification_history_old").
Drop constraints in notification_history that are prefixed with "nh_".

-- Run sanity checks on data in notification_history_pivot
-- 1. Ensure same number of entries in notification_history and notification_history_pivot
-- If not then reconcile entries and add remaining entries to notification_history

-- When sure data in new notification_history table are ok:
ALTER TABLE notification_history_old DROP CONSTRAINT notification_history_pkey; -- May not need this step.
DROP TABLE notification_history_old;

-- Must rename primary key on new notification_history table or will get issues running this script in the future.
-- This is not very nice.
ALTER TABLE notification_history DROP CONSTRAINT notification_history_pivot_pkey;
ALTER TABLE notification_history ADD PRIMARY KEY (id); -- Will create a new primary key named "notification_history_pkey".

-- Note that the only impact of these changes