title: Alter an Existing Column in SQL Server based on the contents of another existing column in the table
body: <p>I am trying to alter the contents of an existing column in SQL Server based on the contents of another column in the same table. There is already some data in the column to be updated which I wish to retain if none of the cases described below apply.</p>
  <p>So far I have pieced together the below statement but something if not many things are clearly being missed.</p>
  <pre><code> Select 'Postal Code', 'Packaging Code',
   From [Clean Report]
       Alter Table [Clean Report]
          CASE 
              when [Postal Code, Clean Report] = '55419-4709'
                  then [Packaging Code, Clean Report] = '079111123'
          Else
              when [Postal Code, Clean Report] = '80222'
                  then [Packaging Code, Clean Report] = '809088899'
          Else (Leave what was already populated in 'Packaging Code, Clean Report Column'
  </code></pre>
  <p>So ideally I would end up with two hard coded values for the specific cases described above and then retain the data that was already populated in the [Packaging Code] Column where the cases above did not apply.</p>
  <p>Any assistance is much appreciated!</p>