One of the beauties of the SQL language in Oracle is that it can so easily be extended by writing functions that SQL can call. Typically in PL/SQL, but for special cases, it might also be in C or in Java. With the new multilingual engine, it’ll be possible in future versions to write stored procedures and functions in multiple languages.
But the thing to note is that SQL and PL/SQL are executed by two different engines, each with small differences, for example, how variables, datatypes, and memory are handled. Every time SQL calls a PL/SQL function, or vice versa PL/SQL executes ...
