row_to_json to get all the first and last days of the current month

first_last.sql

WITH first_day AS (SELECT date_trunc('MONTH', NOW()) :: DATE AS first_date),
     last_day AS (SELECT (date_trunc('MONTH', (SELECT * FROM first_day)) + INTERVAL '1 MONTH' -
                          INTERVAL '1 DAY') :: DATE AS last_date)

SELECT row_to_json(first_last)
FROM (SELECT first_day.*, last_day.*
      FROM first_day,
           last_day) first_last;