Introduction to PLSQL

Introduction to PL/SQL Lecture 4 [Part 1]

Emma-Jane Phillips-Tait [Akhtar Ali]

Overview

of next 3 sessions

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Overview

of PL/SQL

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Development of a coded block



Interacting with an Oracle Database

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Controlling PL/SQL process flow

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Cursor handling

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Error handling

Session 1 

Using PL/SQL to access

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Variable assignment

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Overview

Oracle

of the next 2 weeks

Re-visiting 





SQL

Instructions to Oracle identifying the information you wish to select, insert, delete or update SQL*Plus is Oracle's version of the SQL standard Notes on SQL are on Blackboard

PL/SQL - introduction 

 



Procedural extension allowing for modularity, variable declaration, loops and logical constructs. Allows for advanced error handling Communicates natively with other oracle database objects. Managed centrally within the Oracle database.

Other

Databases



All have procedural facilities

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SQL is not functionally complete 

Lacks full facilities of a programming language

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So top up functionality by embedding SQL in a procedural language

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PL/SQL techniques are specific to Oracle 

but procedures and functions can be ported to other systems

Why 

use PL/SQL

Manage business rules ± through middle layer application logic.



Generate

code for triggers

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Generate

code for interface

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Enable database-centric client/server applications

Centralised V¶s De-centralised

Begin : End;

Server

Common copy of executed code  one copy to maintain

Begin

Begin

Begin

:

:

:

End;

End;

End;

Multiple copies of executable code on the decentralised system  multiple copies to maintain leading to increase difficulty in maintaining the system

Server

Advantages of using PL/SQL to access Oracle 

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PL/SQL is managed centrally within the database Code is managed by the DBA and execution privileges are managed in the same was as with other objects

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PL/SQL objects are first-class Oracle DB objects

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Easy to read 

With

modularity features and error handling

Centralised control 

Enables DBA to: 

Specify rules in one place (as procedure, function, package in PL/SQL)



Force user access through the predefined PL/SQL so users cannot write their own procedural code and use this instead. 

Define for instance security privileges giving users access to table(s) only through a particular procedure

Using PL/SQL as a programming language 

Permits all operations of standard programming languages e.g.  

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Provides loops for controlling iteration 

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Conditions IF-THEN-ELSE-END IF; Jumps GOTO

LOOP-EXIT; WHEN-END LOOP; FOR-END LOOP; WHILE-END LOOP

Allows extraction of data into variables and its subsequent manipulation

Modules in PL/SQL There are 4 types of modules in PL/SQL  Procedures ± series of statements may or may 





not return a value Functions ± series of statements must return a single value Triggers ± series of PL/SQL statements (actions) executing after an event has triggered a condition (ECA) Packages ± collection of procedures and function that has 2 parts: 

a listing and a body.

Procedures Creation command

Create or replace procedure sample1 as

Variable declarations

v_num1 constant number := 2.5; v_num2 constant number := 4; v_product number; BEGIN

Body of code

v_product := v_num1 * v_num2; END;

Use of Data-Types  

 

Number ± used to store any number Char(size) & varchar2(size) e.g.: char(10) ± used to store alphanumerical text strings, the char data type will pad the value stored to the full length declared. Date ± used to store dates Long ± used to store large blocks of text up to 2 gigabytes in length (limited operations)

More data-types 

Long raw ± stores large blocks of data stored in binary format

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Raw

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Rowid

± stores smaller blocks of data in binary formal ± used to store the special format of rowid¶s on the database

Non-database Data Types 

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DEC, DECIMAL, REAL, INTEGER, INT ± these are numerical data types that are a subset of number. Binary_integer ± binary format for number type but can not be stored in database unless con verted first.

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Character ± same as char

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Boolean ± true/false value

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Table/record ± tables can be used to store the equi valent of an array while records store the variables with composite data types.

Using SQL in procedures 

Select values into PL/SQL variables 

using INTO

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Record.element



%rowtype

notation will address components of tuples (dot notation) allows full rows to be selected into one variable

V_employee employee%rowtype

Empid

empname addr1

addr2

addr3

postcode

grade

salary

Example Declare

v_employee

employee%rowtype;

Begin select *

Selects entire row of data into 1 variable called v_employee

into v_employee from employee where empid = 65284;

update employee set salary = v_employee.salary + 10000 where empid = v_employee.empid; end

Is updating the value of salary based on selected element of a variable

Cursor overview 

Very powerful in PL/SQL modules

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Allows more than one set of data to be retrieved and accessed at the same time in loops

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Sets are created by executing SQL statements embedded in the PL/SQL code

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Cursor attributes - %notfound, %rowcount, %found & %isopen

Error handling 

Prevents database locking

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Ensures that errors are presented to the user in a sensible format

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Makes code robust

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Essential when using PL/SQL as formal programming language or interfacing with Oracle applications.