Tài liệu overview of PL / SQL pptx

Overview of PL/SQL
18
Introduction to Oracle: SQL and PL/SQL Using Procedure Builder18Ć2
Schedule: Timing Topic
20 minutes Lecture
20 minutes Total
Overview of PL/SQL 18Ć3
Objectives
This lesson provides an overview of how to create and use PL/SQL program
units and subprograms using Oracle Procedure Builder.
At the end of this lesson, you should be able to
D Determine the benefits of accessing the Oracle7 database with PL/SQL.
D Describe basic PL/SQL program constructs.
D Describe the Oracle Procedure Builder tool.
Introduction to Oracle: SQL and PL/SQL Using Procedure Builder18Ć4
Technical Note:
Examples of procedural programming languages are C and FORTRAN,
which are considered 3GLs. Procedural languages afford direct control over
processing; the programmer must encode exactly how a particular operation
is to be done.
SQL is non-procedural and a 4GL. Non-procedural languages are generally
easier to use, but at the expense of processing control. The programmer
states the database operation that needs to be done, and the Oracle7 Server
determines how to do it.
PL/SQL is a hybrid language that uses SQL to access the database, but
allows explicit processing control on top of SQL. Therefore, PL/SQL
affords the best of both worlds.
Overview of PL/SQL 18Ć5
Overview
What Is PL/SQL?
PL/SQL (Procedural Language/SQL) is an extension to SQL, incorporating many of

the design features of programming languages of recent years. It allows the data
manipulation and query statements of SQL to be included within block-structured and
procedural units of code, making PL/SQL a powerful transaction processing
language.
Benefits from PL/SQL
You can take advantage of the procedural capabilities of PL/SQL, which are
unavailable in SQL.
Modularize Program Development
D Group logically related statements within blocks.
D Nest sub-blocks inside larger blocks to build powerful programs.
D Break down a complex problem into a set of manageable, well-defined, logical
modules, and implement them with blocks.
Declare Identifiers
D Declare variables, constants, cursors, and exceptions, and then use them in SQL
and procedural statements.
D Declare variables belonging to simple and composite datatypes.
D Declare variables dynamically based upon the data structure of tables and
columns in the database.
Program with Procedural Language Control Structures
D Execute a sequence of statements conditionally.
D Execute a sequence of statements iteratively in a loop.
D Process individually the rows returned by a multiple-row query with an explicit
cursor.
D Combine PL/SQL with Oracle tools, such as Developer/2000 Forms, to group
associated commands together to control execution.
Handle Errors
D Process Oracle7 Server errors with exception handling routines.
D Declare user-defined error conditions and process them with exception handling
routines.
Continued

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder18Ć6
Overview of PL/SQL 18Ć7
Overview continued
Benefits of PL/SQLĊcontinued
Portability
D Since PL/SQL is native to Oracle, you can move programs to any host
environment that supports Oracle and PL/SQL.
D You can also move code between the Oracle7 Server and your application
environment using Procedure Builder’s drag-and-drop capabilities.
Integration
D PL/SQL plays a central role to both the Oracle7 Server (through stored
procedures, database triggers, and packages) and Oracle development tools
(through Developer/2000 component triggers).
D Variables and datatypes in PL/SQL and SQL are compatible. Therefore, PL/SQL
bridges the gap between convenient access to database technology and the need
for procedural programming capabilities.
Improve Performance
D PL/SQL can improve the performance of an application. The benefits differ
depending upon the execution environment.
D PL/SQL groups SQL statements together within a single block and sends the
entire block to the server in a single call, therefore reducing network traffic.
Introduction to Oracle: SQL and PL/SQL Using Procedure Builder18Ć8
Overview of PL/SQL 18Ć9
PL/SQL Block Structure
A basic PL/SQL block of code can contain up to three parts. The order in which the
sections of the blocks are written is shown below.
Section
Description Inclusion
Declarative Contains all variables, constants, cursors,
and user-defined exceptions that will be

referenced within the Executable section.
Optional
Executable Contains SQL statements to manipulate
data in the database and PL/SQL
statements to manipulate data in the block.
Mandatory
Exception Handling Specifies the actions to perform when
errors and abnormal conditions arise
within the Executable section.
Optional
Note: In PL/SQL, an error or warning is called an exception.
Section keywords DECLARE, BEGIN, and EXCEPTION are not followed by
semicolons. However, END and all other PL/SQL statements do require a semicolon
to terminate the statement. You can string statements together on the same line.
However, this method is not recommended for clarity or editing.
Introduction to Oracle: SQL and PL/SQL Using Procedure Builder18Ć10
Class Management Note:
In the classroom, the database uses PL/SQL version 2.3, while Procedure
Builder uses PL/SQL version 1.5. Some apparent differences are datatypes,
comparison operators, and composite datatypes.
Overview of PL/SQL 18Ć11
PL/SQL Block Structure continued
Every unit of PL/SQL comprises one or more blocks. These blocks can be entirely
separate or nested one within another. Therefore, one block can represent a small part
of another block, which in turn can be part of the whole unit of code.
PL/SQL Program Constructs
The following list outlines a variety of different PL/SQL program constructs using
the basic PL/SQL block. They are available based on the environment where they are
executed.
Program

Construct
Description Availability
Anonymous Block Unnamed PL/SQL block that is
embedded within an application or
is issued interactively.
All PL/SQL
environments.
Stored Procedure or
Function
Named PL/SQL block that can
accept parameters and can be
invoked repeatedly.
Oracle7 Server with
Procedural Extension.
Application
Procedure or
Function
Named PL/SQL block that can
accept parameters and can be
invoked repeatedly.
Components of
Developer/2000, for
example Forms.
Package Named PL/SQL module that
groups together related procedures,
functions, and identifiers.
Oracle7 Server with
Procedural Extension.
Database Trigger PL/SQL block that is associated
with a database table and is fired

automatically.
Oracle7 Server with
Procedural Extension.
Application Trigger PL/SQL block that is associated
with an application event and is
fired automatically.
Components of
Developer/2000, for
example Forms.
Note: A function is similar to a procedure, except that a function must return a
value.
Introduction to Oracle: SQL and PL/SQL Using Procedure Builder18Ć12
Overview of PL/SQL 18Ć13
PL/SQL Block Structure continued
The two types of constructs covered in this course are anonymous blocks and
subprograms.
Anonymous Blocks
Anonymous blocks are unnamed blocks. They are declared at the point in an
application where they are to be executed and are passed to the PL/SQL engine for
execution at runtime. You can embed an anonymous block within a precompiler
program and within SQL*Plus or Server Manager. Triggers in Developer/2000
components consist of such blocks.
Subprograms
Subprograms are named PL/SQL blocks. You can declare them either as procedures
or as functions. Procedures perform actions, and functions return values.
Developer/2000 components allow you to declare procedures and functions as part of
the application (a form or report), and call them from other procedures, functions, and
triggers.
Introduction to Oracle: SQL and PL/SQL Using Procedure Builder18Ć14
Overview of PL/SQL 18Ć15

The PL/SQL Environment
PL/SQL is not an Oracle product in its own right; it is a technology employed by the
Oracle7 Server and by certain Oracle tools. Blocks of PL/SQL are passed to and
processed by a PL/SQL engine, which may reside within the tool or within the
Oracle7 Server. The engine used depends on where the PL/SQL is being invoked.
PL/SQL Engine at the Oracle7 Server
When you submit blocks from a Pro* program, user-exit, SQL*Plus, or Server
Manager, the PL/SQL engine in the Oracle7 Server processes them. It breaks the SQL
within the block into separate statements and sends them to the SQL Statement
Executor. This means that a single transfer is required to send the block from the
application to the Oracle7 Server, thus improving performance especially in a
client-server network. Stored subprograms can be referenced by any number of
applications connected to the database.
PL/SQL in Oracle Tools
Many Oracle tools, including Developer/2000, have their own PL/SQL engine, which
is independent of the engine present in the Oracle7 Server.
The engine filters out SQL statements and sends them individually to the SQL
Statement Executor in the Oracle7 Server. It processes the remaining procedural
statements in the Procedural Statement Executor, which is within the PL/SQL engine.
The Procedural Statement Executor processes data that is local to the application (that
is already inside the client environment, rather than the database). This reduces work
sent to the Oracle7 Server and the number of memory cursors required.
Note: Procedures and functions declared as part of a Developer/2000 application are
distinct from those stored in the database, although their general structure is
the same. Stored subprograms are database objects and are stored in the Data
Dictionary. They can be accessed by any number of applications.
Application subprograms pass blocks to that application’s local PL/SQL
engine. Work is done at the application site, not at the server site.
Introduction to Oracle: SQL and PL/SQL Using Procedure Builder18Ć16
Overview of PL/SQL 18Ć17

About Procedure Builder
Oracle Procedure Builder is a tool you can use to create, execute, and debug PL/SQL
programs used in your application tools, such as a form or a report, or on the Oracle7
Server through its graphical interface.
Integrated PL/SQL Development Environment
Procedure Builder’s development environment contains a built-in editor for you to
create or edit subprograms. You can compile, test, and debug your code.
Unified ClientĆServer PL/SQL Development
Application partitioning through Procedure Builder is available to assist you with
distribution of logic between client and server. Users can drag and drop a PL/SQL
program unit between the client and the server.
Class Management Note:
Oracle Procedure Builder is sold with Developer/2000 or as a separate
product.
Introduction to Oracle: SQL and PL/SQL Using Procedure Builder18Ć18