title: generate Fiscal_day_date based on calendar date in Bigquery
body: <p>we have a date dimension table where all the calendar and fiscal dates for 30 years are populated. Now we need to add new column as Fiscal_day_date and our Fiscal year starts from Sep-01. we need output as mentioned below :</p>
  <p><img src="https://i.stack.imgur.com/JyIJF.png" alt="enter image description here" /></p>