15.2 Review of PL/SQL Block Structure
Chapter 1, Introduction to PL/SQL , provided a brief introduction to the PL/SQL block and its structure. Before we explore the construction of modules in PL/SQL, let's take a more detailed look at the PL/SQL block.
PL/SQL is a block-structured language. Each of the basic programming units you write to build your application is (or should be) a logical unit of work. The PL/SQL block allows you to reflect that logical structure in the physical design of your programs.
The block determines both the scope of identifiers (the area of code in which a reference to the identifier can be resolved) and the way in which exceptions are handled and propagated. A block may also contain nested sub-blocks of code, each with its own scope.
There is a common block structure to all the different types of modules. The block is broken up into four different sections, as follows:
Figure 15.1 shows the structure of the PL/SQL block.
Figure 15.1: The PL/SQL block structure for procedures and functions
15.2.1 Sequence of Section Construction
The ordering of the sections in a block corresponds to the way you would write your programs and the way they are executed.
The declaration and exception sections are optional in any PL/SQL block, but you must always have at least one executable statement in a block.
15.2.2 PL/SQL Block Structure Examples
Figures Figure 15.2 through Figure 15.4 illustrate several different ways that PL/SQL blocks can be constructed.
Figure 15.2: A procedure containing all four sections
Figure 15.3: A function without an exception section
Now that you understand the basic components of a PL/SQL block, let's explore the ways you can use this structure in your programming.
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