>Prolog is Turing complete, SQL is not.

This is actually not true. Behold, a cyclic tag system in SQL:2003-conformant SQL:

http://wiki.postgresql.org/wiki/Cyclic_Tag_System

Here's a blog diving into more detail: http://blog.coelho.net/database/2013/08/17/turing-sql-1.html

Although this is less strictly conforming.

The original thread was in the context of SQLite, which is trivially of equivalent computational power.

However, again: you should probably use Prolog.