Oracle PL/SQL Programming, 5th 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 “statically typed programming language” (see the following sidebar for a definition). PL/SQL offers a comprehensive set of predefined scalar and composite datatypes, and you can create your own user-defined types (also known as abstract datatypes). Many of the PL/SQL datatypes are not supported by database columns, such as Boolean and NATURAL, but within PL/SQL code, these datatypes are quite useful.

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 BOOLEAN is (FALSE, TRUE);

  type NUMBER is NUMBER_BASE;
  subtype INTEGER is NUMBER(38,);

When it comes to datatypes, PL/SQL supports the “usual suspects” and a whole lot more. This section provides a quick overview of the various predefined datatypes. They are covered in detail in Chapters 8 through 13, Chapter 15, and Chapter 26; you will find detailed references to specific chapters in the following sections.

What Does “Static Typing” Mean?

A programming language uses static typing, also called strong typing, if type checking is performed at compile-time as opposed to at runtime. Some programming languages that use static typing include PL/SQL, Ada, C, and Pascal. A dynamically typed programming language, like JavaScript, ...