PL/SQL is a procedural language extension of SQL, designed to enhance the capabilities of SQL by adding procedural programming constructs. It provides a powerful way to write complex database applications.
PL/SQL Architecture
The PL/SQL architecture is a multi-layered structure that includes the following components:
Physical Layer: This layer is responsible for the physical storage of PL/SQL source code and compiled code. It interacts with the operating system and database engine to manage storage and execution.
Logical Layer: This layer handles the compilation and execution of PL/SQL code. It includes the PL/SQL compiler, which translates PL/SQL source code into executable code.
Runtime Environment: This layer provides the runtime environment for executing PL/SQL code. It manages memory allocation, exception handling, and other runtime services.
PL/SQL Block Structure
A PL/SQL block is the basic unit of code in PL/SQL. It consists of three main sections:
DECLARE Section (Optional):
Declares variables, constants, cursors, and exception handlers.
Used to define data structures and initialize variables.
BEGIN Section (Mandatory):
Contains the executable statements of the block.
This is where the actual processing logic is implemented.
EXCEPTION Section (Optional):
Handles exceptions that may occur during the execution of the block.
It allows you to gracefully handle errors and provide informative messages.
Example:
DECLARE
v_salary NUMBER(10,2);
BEGIN
SELECT salary INTO v_salary
FROM employees
WHERE employee_id = 101;
DBMS_OUTPUT.PUT_LINE('Salary: ' || v_salary);
EXCEPTION
WHEN NO_DATA_FOUND THEN
DBMS_OUTPUT.PUT_LINE('Employee not found');
END;
/
Key Points:
PL/SQL blocks can be anonymous or named.
Anonymous blocks are executed once and then discarded.
Named blocks are stored in the database as procedures, functions, or packages.
PL/SQL provides a rich set of data types, control flow statements, and built-in functions.
By understanding the PL/SQL architecture and block structure, you can write efficient and maintainable database applications.
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