SQL is a very, very poor implementation of relational algebra. For example, the output of an SQL query is not even a valid relation variable (in E. F. Codd's te

SQL is a very, very poor implementation of relational algebra. For example, the output of an SQL query is not even a valid relation variable (in E. F. Codd's terminology). If you want to look at how SQL might have looked if it had been relational, take a look at "Tutorial D", the language proposed in a book called The Third Manifesto, by Hugh Darwen and C. J. Date: http://thethirdmanifesto.com/ http://thethirdmanifesto.com/. There are several experimental implementations.