From: hugo@perFact.REMOVETHIS.info.INVALID   
      
   Hi Tom,   
      
   The CASE expression has two syntaxes:   
      
   1:   
   CASE   
     WHEN  THEN    
   { WHEN  THEN   ... }   
   [ ELSE  ]   
   END   
      
   2:   
   CASE    
     WHEN  THEN    
   { WHEN  THEN   ... }   
   [ ELSE  ]   
   END   
      
   The second is defined to be equivalent to the former, where each WHEN   
    is replaced by WHEN  = .   
      
   >SELECT PersonID = CASE o.ID WHEN NULL THEN o2.ID ELSE o.ID END   
      
   As a result, the expression above is valid syntax (both o.ID and NULL   
   are valid scalar expressions) - but nonsense. A comparison with NULL   
   will never evaluate to True, so this whole fragment is logically   
   equivalent to   
      SELECT o.ID   
      
   >SELECT PersonID = CASE o.ID WHEN NOT NULL THEN o2.ID ELSE o.ID END   
   and   
   >SELECT PersonID = CASE o.ID WHEN IS NOT NULL THEN o2.ID ELSE o.ID END   
      
   These are both invalid syntax, because neither NOT NULL nor IS NOT   
   NULL is a valid scalar expression.   
   --   
   Hugo Kornelis, SQL Server MVP   
   My SQL Server blog: http://sqlblog.com/blogs/hugo_kornelis   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)