3.4.2 Numeric Literals

Numeric literals can be integers or real numbers (a number that contains a fractional component). Note that PL/SQL considers the number 154.00 to be a real number, even though the fractional component is zero and the number is actually an integer. Internally, integers and reals have a different representation, and there is some small overhead involved in converting between the two.

You can also use scientific notation to specify a numeric literal. Use the letter "E" (upper- or lowercase) to multiply a number by 10 to the nth power—for example, 3.05E19, 12e-5.

3.4.3 Boolean Literals

Oracle provides two literals to represent Boolean values: TRUE and FALSE. These values are not strings; you should not put quotes around them. Use Boolean literals to assign values to Boolean variables, as in:

DECLARE

enough_money BOOLEAN; -- Declare a Boolean variable

BEGIN

enough_money := FALSE; -- Assign it a value

END;

You do not, on the other hand, need to refer to the literal value when checking the value of a Boolean expression. Instead, just let that expression speak for itself, as shown in the conditional clause of the following IF statement:

DECLARE

enough_money BOOLEAN;

BEGIN

IF enough_money

THEN

...

3.5 The Semicolon Delimiter

A PL/SQL program is made up of a series of declarations and statements. These are defined logically, as opposed to physically. In other words, they are not terminated with the physical end of a line of code; instead, they are terminated with a semicolon (;). In fact, a single statement is often spread over several lines to make it more readable. The following IF statement takes up four lines and is indented to reinforce the logic behind the statement:

IF salary < min_salary (2003)

THEN

salary := salary + salary*.25;

END IF;

There are two semicolons in this IF statement. The first semicolon indicates the end of the single executable statement within the IF-END IF construct. The second semicolon terminates the IF statement itself. This same statement could also be placed on a single physical line and have exactly the same result:

IF salary < min_salary (2003) THEN salary := salary + salary*.25; END IF;

The semicolons are still needed to terminate each logical, executable statement, even if they are nested inside one another. Unless you're trying to create unreadable code, I suggest that you not combine the different components of the IF statement on a single line. I also recommend that you place no more than one statement or declaration on each line.

3.6 Comments

Inline documentation, otherwise known as comments, is an important element of a good program. While this book offers many suggestions on how to make your program self-documenting through good naming practices and modularization, such techniques are seldom enough by themselves to communicate a thorough understanding of a complex program.

PL/SQL offers two different styles for comments: single-line and multiline block comments.

3.6.1 Single-Line Comment Syntax

The single-line comment is initiated with two hyphens ( -- ), which cannot be separated by a space or any other characters. All text after the double hyphen to the end of the physical line is considered commentary and is ignored by the compiler. If the double hyphen appears at the beginning of the line, the whole line is a comment.

Remember: the double hyphen comments out the remainder of a physical line, not a logical PL/SQL statement. In the following IF statement, I use a single-line comment to clarify the logic of the Boolean expression:

IF salary < min_salary (2003) -- Function returns min salary for year.

THEN

salary := salary + salary*.25;

END IF;