Sales to Date versus Last Month

SELECT strftime('%d', o."CloseDate") 'Day',
       SUM(case when (strftime('%Y-%m', o."CloseDate") = '2015-05') then ifnull(o."Amount",0) else 0 end) 'Amount (Prev Month)',
       SUM(case when (strftime('%Y-%m', o."CloseDate") = '2015-06') then ifnull(o."Amount",0) else 0 end) 'Amount (Current Month)'
 FROM "Opportunity" o
 WHERE o."IsClosed"=true AND
       o."IsWon"=true AND
       o."CloseDate">='2015-05-01' and o."CloseDate"<='2015-06-30'
 GROUP BY strftime('%d', o."CloseDate")
  

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