Oracle PL/SQL Programming, Third Edition

Overview of PL/SQL Datatypes

Whenever you declare a variable or a constant, you must assign it a datatype. (PL/SQL is, with very few exceptions, a “strongly typed” language; see the sidebar for a definition.) PL/SQL offers a comprehensive set of predefined scalar and composite datatypes, and starting with Oracle8 you can create your own user-defined types (also known as abstract datatypes).

What Does “Strongly Typed” Mean?

“A strongly typed programming language is one in which each type of data (such as integer, character, hexadecimal, packed decimal, and so forth) is predefined as part of the programming language, and all constants or variables defined for a given program must be described with one of the data types. Certain operations may be allowable only with certain data types. The language compiler enforces the data typing and use compliance. An advantage of strong data typing is that it imposes a rigorous set of rules on a programmer and thus guarantees a certain consistency of results. A disadvantage is that it prevents the programmer from inventing a data type not anticipated by the developers of the programming language and it limits how “creative” one can be in using a given data type.” (Definition courtesy of http://www.whatis.com)

Virtually all of these predefined datatypes are defined in the PL/SQL STANDARD package. Here, for example, are the statements that define the Boolean datatype and two of the numeric datatypes:

create or replace package STANDARD is              

  type ...