title: T-SQL Query will not return 0 value for a Sum
body: <p>I have a query where I'm calculating Days of Therapy for medications. I want to have 0 values to show for months that have no data. Currently the query returns no record if the Sum is 0. Can't seem to figure this out.  See the Query Below:</p>
  
  <p>If I were to comment out identifiers related to the DOT_ALL table along with the Where Clause I get 60 rows, 1 for each month for the past 5 years. However, otherwise i get only 57 for the drug in  the Where Clause since there are not DOTs for Aug 2016, April 2016 and Jan 2015.</p>
  
  <p>Thanks in advance.</p>
  
  <pre><code>----------------------------------------------------------------------------
  
  SELECT
      AMS.[Medication Name]
      , SUM(AMS.DOT) AS DOT
      ,  PD.[Patient Days]
      , PD.[Month_Name]
      , PD.[Fiscal_Month]
      , PD.[Accounting_Year]
      , PD.[Year]
  
  FROM
      DW_PROD.dbo.Patient_Days_By_Month PD 
      Left JOIN [DW_PROD].[dbo].[DOTS_All] AMS ON (PD.Month_Name = AMS.Month AND PD.Year = AMS.Year)
  
  WHERE
      [Medication Name] = 'CEFUROXIME'
  
  GROUP BY
      AMS.[Medication Name]
      , PD.[Patient Days]
      , PD.[Month_Name]
      , PD.[Fiscal_Month]
      , PD.[Accounting_Year]
      , PD.[Year]
  
  ORDER BY
      ACCOUNTING_YEAR
      ,FISCAL_MONTH
  </code></pre>
  
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