PL - SQL Structure

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.

Each PL/SQL block has up to four different sections (some are optional under certain circumstances):

The block structure is at the core of two key concepts and features of the PL/SQL language:

Modularization - The PL/SQL block is the basic unit of work from which modules, such as procedures and functions, are built. The ability to modularize is central to successfully developing complex applications.

Scope - The block provides a scope or context for logically related objects. In the block, you group together declarations of variables and executable statements that belong together.

You can create anonymous blocks (blocks of code that have no name) and named blocks, which are procedures and functions. Furthermore, you can build packages in PL/SQL that group together multiple procedures and functions.

Header - Relevant for named blocks only. The header determines the way the named block or program must be called.

Declaration section - The part of the block that declares variables, cursors, and sub-blocks that are referenced in the execution and exception sections.

Execution section - The part of the PL/SQL block containing the executable statements, the code that is executed by the PL/SQL runtime engine.

Exception section - The section that handles exceptions to normal processing (warnings and error conditions).

The ordering of the sections in a block corresponds to the way you would write your programs and the way they are executed:

Step 1 - Define the type of block (procedure, function, anonymous) and the way it is called (header).

Step 2 - Declare any variables used in that block (declaration section).

Step 3 - Use those local variables and other PL/SQL objects to perform the required actions (execution section).

Step 4 - Handle any problems that arise during the execution of the block (exception section).