The way I see it:  
 - SQL *language* questions belong on [StackOverflow][1]  
 - Database *server* questions belong on [ServerFault][2]  
 - Database *tuning* questions belong on [dba.SE][3]


  [1]: http://stackoverflow.com/
  [2]: https://serverfault.com/
  [3]: https://dba.stackexchange.com/