This is actually not true. Prolog is Turing complete, SQL is not. WITH RECURSIVE is limited to cases where you could basically use a simple foreach loop. The postgres manual has this to say:

> Note: Strictly speaking, this process is iteration not recursion, but RECURSIVE is the terminology chosen by the SQL standards committee.

That said, the feature was to some degree inspired by datalog.

EDIT: I should probably clarify, many dbmses probably have extensions that do make SQL turing complete, and the current standard is if you count stored procedures I guess. But CTEs themselves are more limited than what Prolog does.