Identifiers(contd..)

Reserved Words
Some identifiers, called reserved words, have a special syntactic meaning to PL/SQL.They are identifiers that Oracle sets aside for internal
use. If they are used in application development, Oracle will interpret them as defined by Oracle, not according to your definition. This can cause some serious problems if
the reserved words are used for purposes such as variable names.Often, reserved words are written in upper case for readability.
Trying to redefine a reserved word causes a compilation error. Instead, you can embed reserved words as part of a longer identifier

Special Characters

In addition to reserved words, there are keywords that have special meaning in PL/SQL.They are called as special characters. Special characters are identifiers that PL/SQL interprets as a
command or that have some other special purpose. Using these characters in PL/SQLin a way that is contrary to their purpose will result in an error or incorrect processing
of code.

Predefined Identifiers

Identifiers globally declared in package STANDARD, such as the exception INVALID_NUMBER, can be redeclared. However, redeclaring predefined identifiers is error prone because your local declaration overrides the global declaration.

Quoted Identifiers

Identifiers can include nonstandard characters and spaces when
they are enclosed in double quotes. The following quoted identifiers are supported:
“John’s Cursor”
“Mine/Yours”
“Begin”
Quoted identifiers are case sensitive and can even include reserved words that are not otherwise allowed. We highly recommend against using these nonstandard identifiers. Unless working with an extreme situation where they are somehow required, they will only cause problems.

The maximum size of a quoted identifier is 30 characters not counting the double quotes. Though allowed, using PL/SQL reserved words as quoted identifiers is a poor programming practice