Database Reference
In-Depth Information
of people who live in Portugal, and some can hold a list of things, like the birth dates of my
family members.
Variable Naming
Like a SQL or database data type, PL/SQL variables must follow the identifier naming
rules:
• A variable name must be less than 31 characters in length.
• A variable name must start with an uppercase or lowercase ASCII letter:
A
-
Z
or
a
-
z
. PL/
SQL is not case-sensitive.
• A variable name may be composed of 1 letter, followed by up to 29 letters, numbers, or
the underscore (_) character. You can also use the number (#) and dollar sign ($) characters.
Declaring, declaration, declaration section: Declaring a variable means naming it and de-
fining its datatype. With few exceptions, variables must be declared prior to use. In PL/
SQL, these designations most often occur in a separate section of the program called the
declaration section. Declarations are not, strictly speaking, “statements” themselves.
String: Some amount of textual data—that is, characters, words, spaces, punctuation, and
sometimes numerals. A string can contain zero, one, or more individual characters. String
values can be stored in variables with the appropriate datatype, such as VARCHAR2. String
values are bounded by single quotes, as in 'Hello Everybody'.
NULL :A special value that represents the absence of a real value. Let's further define
NULL:
• NULL is not equal to anything, not even NULL.
• NULL is not less than or greater than anything else, not even NULL.
• NULL means nothing knows, not even NULL.
Boolean :
A class of variables and commands for working with the “truth values” of true
and false. Oracle Booleans, which are available in PL/SQL but not SQL, actually have
three possible values, TRUE, FALSE, and NULL.
Literal :
A literal is a value that is not represented by an identifier; it is simply a value.. Lit-
erals may be string, numeric, or Boolean values. Examples: 106700, TRUE, ' Ajit Singh'
Expression :
A formula that evaluates some value at runtime based on one or more other
values. Examples: b + c, NOT done.
