Embracing SQL in Postgres(rob.conery.io)

  SELECT sku, sum(price)
  FROM invoice_items
  WHERE date_part('month',created_at) = 9
  GROUP BY sku

  WITH items AS (
    SELECT *, date_part('month',created_at) AS month
    FROM invoice_items
  )
  SELECT sku, month, sum(price)
  FROM items
  WHERE month in (7,8,9)
  GROUP BY sku, month

  WITH items AS (
    SELECT
        *
        ,date_part('year',created_at)    AS year
        ,date_part('month',created_at)   AS month
        ,date_part('quarter',created_at) AS quarter
    FROM invoice_items
  )
  SELECT DISTINCT
      sku
      ,year
      ,month
      ,quarter
      ,sum(price) OVER (PARTITION BY year)          AS yearly_total
      ,sum(price) OVER (PARTITION BY year, month)   AS monthly_total
      ,sum(price) OVER (PARTITION BY year, quarter) AS quarterly_total
      ,sum(price) OVER (PARTITION BY month)         AS month_number_total
      ,sum(price) OVER (PARTITION BY quarter)       AS quarter_number_total
  FROM items
  ORDER BY 1,2,3,4