title: CASE checks for NULL values inside IN clause
body: <p>Can I use CASE inside IN statement? I am using mysql server and below is the query.</p>
  
  <pre><code>SELECT Id from Tenant 
  where TenantId IN (
                      CASE WHEN 'someVariable' is NULL 
                      THEN  (select customer_id from Partners where partner_id = 'abc') 
                      ELSE ('xyz1','xyz2','xyz3') 
                      END
                    )
  </code></pre>
  
  <p>This throws error : 
      <strong><code>Error Code: 1241. Operand should contain 1 column(s)</code></strong></p>
  
  <p>I need to check for Null value in IN clause and then depend on the result need to either fire select on "Partners" table or just pass a list of predefined strings to IN clause. 
  Thanks in advance.</p>