Chapter 7

1. The words function and procedure are often mixed up. However, there is actually a difference: in a procedure, you can run more than just one transaction. It can, therefore, not be part of a SELECT statement, and has to be executed using the CALL command. In contrast to that, a function has only limited transaction control, and can be part of a SELECT, INSERT, UPDATE, or DELETE statement.
2. Trusted languages limit the programmer's ability to perform system calls. They are therefore considered to be safe. Untrusted languages, however, can perform all kinds of operations, and are therefore only available to superusers in order to ensure that no security leaks are possible.
3. This question is somewhat hard to answer. Nothing is only good or only bad. The same applies to functions. They can help you to achieve your goal faster...