CASE STATEMENT USING MULTIPLE COLUMNS

Your example looks like it would fail for having no comma after colB.

Here is a sample of using a case statement based on multiple columns:

 create table #temp (cola varchar(10), colb varchar(10), colc varchar (10))
 
 insert into #temp
 values 
  ('1', '2', 'both'),
  ('', '', 'neither'),
  ('col1', 'col2', 'both'),
  ('', 'col2', 'justb'),
  ('col1', '', 'justa')
  
 select 
  case
  when cola = '' and colb = '' then 'neither'
  when (cola <> '' and colb <> '') then 'both'
  when (cola = '' and colb <> '') or (colb = '' and cola <> '') then 'Just one'
  end as HowMany,
  colc
 from #temp
  
  
 drop table #temp

and the results are:

 HowMany colc
 both both
 neither neither
 both both
 Just one justb
 Just one justa