According to [Immerman][1], the complexity class associated with [SQL][2] queries is exactly the class of *safe queries* in $\mathsf{Q(FO(COUNT))}$ (first-order queries plus counting operator). 

Is there an extension of SQL (implemented and used in the industry) which captures polynomial time computable queries? If there isn't, is there a reason? Are the queries that are needed in practice usually simple enough that there is no need for a stronger language?

  [1]: http://books.google.ca/books?id=kWSZ0OWnupkC&pg=PA224#v=onepage&q&f=false
  [2]: http://en.wikipedia.org/wiki/SQL