title: Only one expression can be specified in the select list when the subquery is not introduced with EXISTS
body: <p>I've serched google and stackoverflow before posting this. There are many post on this case, but I can't find the problem in my query.</p>
  
  <pre><code>    DECLARE @hipero_a int
  SET @hipero_a = 1
  
  SELECT
  CASE @hipero_a 
  WHEN 1 THEN --month
      (
      SELECT Year(o.AccomplishDate) AS [Rok], Month(o.AccomplishDate) AS [Miesiąc], SUM(oi.Price) AS [Przychód]
      FROM Orders o JOIN OrdersItems oi ON oi.OrderId = o.Id
      WHERE o.State = 0
      GROUP BY Year(o.AccomplishDate), Month(o.AccomplishDate)
      --ORDER BY Year(o.AccomplishDate), Month(o.AccomplishDate) ASC
  )
  WHEN 2 THEN --year
      (
      SELECT Year(o.AccomplishDate) AS [Rok], SUM(oi.Price) AS [Przychód]
      FROM Orders o JOIN OrdersItems oi ON oi.OrderId = o.Id
      WHERE o.State = 0
      GROUP BY Year(o.AccomplishDate)
      --ORDER BY Year(o.AccomplishDate) ASC
      )
      END
  </code></pre>
  
  <p>I get errors:</p>
  
  <blockquote>
    <p>Msg 116, Level 16, State 1, Line 14
    Only one expression can be specified
    in the select list when the subquery
    is not introduced with EXISTS. </p>
    
    <p>Msg
    116, Level 16, State 1, Line 22 Only
    one expression can be specified in the
    select list when the subquery is not
    introduced with EXISTS.</p>
  </blockquote>
  
  <p>What is wrong?</p>