title: How to assign row_number to missing values in SQL
body: <p>I want to assign row_number() to missing values as well. I know that row_number will assign sequence to the non-missing values. How can we approach this problem?</p>
  <h2>Code Snippet</h2>
  <pre class="lang-sql prettyprint-override"><code>SELECT id, date,sum(purchase) as purch, 
  row_number() over(partition by id order by date desc) as rown 
  FROM table 
  where
  date in (current_date(),current_date()-1,current_date()-2)
  OR
  date between current_date()-364 and current_date()-365
  group by id,date
  order by date desc
  </code></pre>
  <hr />
  <p>I want to use the values of sum(purchase) for particular dates, so, I want the row_number for each dates even no purchase has happened at that particular day(value could get replace with NULL).</p>
  <p>output should look like-</p>
  <pre><code>row_number       purchase       date
    1               23         current_date
    2               24         current_date-1
    3               null       current_date-2(let's say this is our missing date data)
    4               23         current_date-364
    5               null       current_date-365(let's say this date is mising in our data)
  </code></pre>