Solution Review: Compute Fortnightly Changes

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/***** The code for data loading is already added. *****/
/*****      Please write your query and press      *****/
/*****      the Run button to see the output       *****/
/*****       of the query you have written.        *****/
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\set start '2017-02-01'
/*****************Write your query here*****************/
with computed_data as
(
  select cast(date as date)   as date,
         to_char(date, 'Dy')  as day,
         coalesce(dollars, 0) as dollars,
         lag(dollars, 2)
           over(
             partition by extract('isodow' from date)
                 order by date
           )
         as dollars_two_weeks_before
    from /*
          * Generate the month calendar, plus a week before
          * so that we have values to compare dollars against
          * even for the first week of the month.
          */
         generate_series(date :'start' - interval '2 weeks',
                         date :'start' + interval '1 month'
                                       - interval '1 day',
                         interval '1 day'
         )
         as calendar(date)
         left join factbook using(date)
)
  select date, day,
         to_char(
             coalesce(dollars, 0),
             'L99G999G999G999'
         ) as dollars,
         case when dollars is not null
               and dollars <> 0
              then round(  100.0
                         * (dollars - dollars_two_weeks_before)
                         / dollars
                       , 2)
          end
         as "Fortnight %"
    from computed_data
   where date >= date :'start'
order by date;
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