title: What does ''?'' mean in SQL Server?
body: <p>I've written this code and someone helped me out but I can't figure out what ''?'' means to the DB engine. It would really help me understand what I've written here.</p>
  
  <pre><code> USE master
   EXEC sp_MSforeachdb 'use ? select ''?'', st.NAME, sc.NAME,         
   sc.system_type_id, db_name()
   FROM sys.tables st
   INNER JOIN sys.columns sc ON st.object_id = sc.object_id
   WHERE (st.name LIKE ''rawp%'' or st.name like ''main'')'
  </code></pre>
  
  <p>I understand I'm searching all db in the instance for the name of the columns and their related tables but I need to understand how ''?'' fits into the Query. Thanks!</p>