Can SQL, Without Extensions, Achieve Turing Completeness?

SQL’s Turing completeness: can it be achieved without extension?

Question: Given SQL's apparent Turing completeness, is it theoretically possible to build a compiler using SQL?

Answer: Yes, SQL is indeed Turing complete even without external extensions like PL/SQL or PSM.

Proof: Andrew Gierth proved in a demonstration that SQL is Turing complete without script extensions. By implementing a cycle marking system (a proven Turing-complete model), he demonstrated that SQL can solve problems recursively. In this context, the key feature is CTE (Common Table Expression), which allows self-referential subexpressions.

Meaning:

The discovery of SQL’s Turing completeness highlights the scalability of this primarily declarative query language. Just as C's templates unexpectedly became Turing-complete, SQL's CTE properties make it a more general language.

Example:

A notable example is the creation of the Mandelbrot Set in SQL, demonstrating the potential of the language in computationally intensive applications.

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