title: Using case statement when joining two values SQL
body: <p>Please refer to the screenshot below</p>
  
  <p><a href="https://i.stack.imgur.com/qZnHL.png" rel="nofollow noreferrer">Screenshot</a></p>
  
  <p>The below query should definitely join the HELD_PARAM and the HELD_VALUE fields together as HEADER</p>
  
  <pre><code>SELECT *
      ,ISNULL(HDR_PARAM, '')  + ISNULL(HELD_VALUE, '') AS HEADER  
  FROM "dbo"."T_table" 
  </code></pre>
  
  <p>I was trying to hardcode one HELD_VALUE to reflect a different result like in the screenshot below. Could someone tell me what's wrong with the query?
  <a href="https://i.stack.imgur.com/zbahN.png" rel="nofollow noreferrer">Screenshot</a></p>
  
  <pre><code>SELECT *,
       ISNULL(HDR_PARAM, '')  + (ISNULL(HELD_VALUE, ''), 
                  CASE WHEN HELD_VALUE = 'Y' THEN 'Z'
                  ELSE HELD_VALUE
      END) AS HEADER
  FROM "dbo"."T_table" 
  </code></pre>