Expert

1-16.

Why does this code compile?

DECLARE
   sysdate NUMBER;
BEGIN
   sysdate := 1;
END;

But this code does not?

DECLARE
   then NUMBER;
BEGIN
   then := 1;
END;

1-17.

How can you get around this restriction and declare SUBTYPEs which are, in effect, constrained? To be specific, I want to declare a subtype called primary_key_t that limits the size of any variable declared with that type to NUMBER(6).

1-18.

The NULL value in Oracle is handled differently from other values. One could even say that there is no such thing as a “NULL value.” (NULL means “indeterminate.”) Name three rules that apply to NULLs when doing comparisons.

1-19.

What special operators does Oracle provide for dealing with NULLs?

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