Tài liệu Summary of PL / SQL pdf

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 26Ć2... It is a language that allows you to combine multiple SQL statements with procedural controls such as identifiers, c

Summary of PL/SQL

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Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 26Ć2

PL/SQL (Procedural Language/SQL) is an extension to SQL It is a language that allows you to combine multiple SQL statements with procedural controls such as identifiers, conditional, and iterative constructs in a PL/SQL block

Benefits from PL/SQL

D Modularize program development by grouping similar concepts together and nesting blocks

D Declare identifiers, for example, variables, constants, and cursors

D Program with procedural language structures, for example, IF statements and loops

D Exception handling for Oracle7 Server errors and user-defined exceptions

D Port code between applications and the Oracle7 Server

D Integrate Oracle7 stored subprograms and application subprograms

D Improve performance by sending a block of code to the server

PL/SQL Block

A PL/SQL block contains code in up to four sections The header section is where you set the name and parameters for named blocks The declarative section is

optional and contains all variables, constants, cursors, and user-defined exceptions that will be referenced within the executable section The executable section is

required and contains SQL statements to manipulate data in the database and PL/SQL statements to manipulate data in the block The exception-handling section is optional and specifies the actions to perform when errors and abnormal conditions arise within the executable section

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

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 26Ć4

Summary continued

Procedures

Procedures are named PL/SQL blocks that store a series of actions for later execution The procedure can contain zero or more parameters, which are arguments that you list when calling the procedure Procedures can either be application specific or stored in the Oracle7 Server

Functions

A function returns a value to the calling environment You must declare the RETURN datatype in the header section of the function definition, and define the value to be returned in the PL/SQL block You can also declare a list of parameters to be passed into the function Functions are called as part of an expression

DML in PL/SQL

You can use DML statements in your PL/SQL blocks Use the SELECT statement to retrieve data from the database

D The SELECT statement contains an additional mandatory clause: the INTO clause In the INTO clause, list the output variables for receiving the data The SELECT statement must return exactly one row or an error will occur

D The INSERT statement adds new rows of data to the table

D The UPDATE statement modifies existing rows in the table

D The DELETE statement removes unwanted rows from the table

D COMMIT ends the current transaction by making all pending changes to the database permanent

D ROLLBACK ends the current transaction by discarding all pending changes

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 26Ć6

Summary continued

IF Conditional Statements

The PL/SQL IF statement is similar to the structure of IF statements in other

procedural languages It allows PL/SQL to perform actions selectively based upon conditions If the controlling Boolean condition is TRUE, the associated sequence of statements is executed; if the controlling Boolean condition is FALSE or NULL, the associated sequence of statements is passed over

Iterative Loop Statements

You can use one of three loop structures to repeat a sequence of statements

D The basic loop consists of the body of statements to be repeated enclosed between

the delimiters LOOP and END LOOP This uncontrolled loop is an infinite loop

that is to be avoided To avoid an infinite loop, add an EXIT statement

D FOR loops have a control statement at the front of the LOOP keyword to

determine the number of iterations PL/SQL performs

D The WHILE loop repeats a sequence of statements until the controlling condition

is no longer TRUE The condition is evaluated at the start of each iteration

Cursors

PL/SQL cursors let you name a private SQL area and access its stored information The cursor directs all phases of processing Explicit cursors are declared and named

by the programmer and manipulated through specific statements within the block’s executable actions Control explicit cursors in a loop with four steps: declare, open, fetch, and close Cursor FOR loops are a shortcut to open the cursor, fetch rows once for each loop iteration, and automatically close the cursor after all rows are

processed

Exception Handling

An exception is an identifier in PL/SQL, raised during the execution of a block that

terminates its main body of actions A block will always terminate when PL/SQL raises an exception, but you specify an exception handler to perform final actions Exceptions can be raised either by the Oracle7 Server or by the user You can either

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 26Ć8

Practice Overview

This practice has you build a PL/SQL-based application to insert, update, and delete records in a video store database and generate a report The database contains only the essential tables

Practice Contents

D Creating procedures and functions

D Inserting, updating, and deleting data

D Incorporating IF statements and loops

D Handling exceptions

Note: If you are new to the class, you can execute the buildvid.sql script in

SQL*Plus to create and populate the tables If you want to drop the work you did in the course summary from the SQL section, you can execute the

dropvid.sql script in SQL*Plus to drop their tables Then, you can execute the buildvid.sql script in SQL*Plus to create and populate the tables.

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 26Ć10

Practice 26

Entity Relationship Diagram

The facing page contains an entity relationship diagram depicting the tables and columns for a small movie rental application

1. Complete the database design by writing subprograms to perform the following actions

a. Create a function named NEW_MEMBER to return the membership number for that new member Be sure to use a sequence generator to create the unique member numbers Check the data dictionary for the sequence name

b. Create a function named NEW_RENTAL to record a new rental based on a member’s last name Return a message with the expected due date If two or more people have the same last name, store the first name, last name, phone, and membership number for all matching last names in the RESULTS table

c. Create a procedure named MEM_TITLES to retrieve all the titles rented by a member Store the results in the RESULTS table

d. If a title is rented, create a reservation for that movie Name your procedure RESERVE_MOVIE

e. When a video is returned, change the rental status for that returned copy When the video is successfully checked in, store a message in the RESULTS table Check the to see if there are reservations for the film title, and store a message in the RESULTS table Name your procedure RETURN_RENTAL

f. If a video is returned damaged, change its status to DAMAGED If that copy was the only copy owned by the store, store a message to buy another copy in the RESULTS table If only one copy remains for rental, store a warning that only one copy is left for rental in the RESULTS table Name your procedure DAMAGED_COPY

g. Create a procedure named TOP_RENTAL to determine the top rental Allow for more than one top rental Store the names and a message of the top rentals

in the RESULTS table

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 26Ć12