RDBMS - UNIT 4.pdf,UNIT THREE AND UNIT FIVE

UNIT IV
PL/SQL: A Programming Language: History–Fundamentals–Block
Structure–Comments – Data Types–Other Data Types–Variable
Declaration–Anchored Declaration-Assignment operation – Bind
Variables–Substitution Variables–Printing in PL/SQL–Arithmetic
Operators. Control Structures and Embedded SQL: Control Structures–
Nested Blocks–SQL in PL/SQL–Data Manipulation –Transaction
Control statements. PL/SQL Cursors and Exceptions: Cursors –
Implicit & Explicit Cursors and Attributes–Cursor FOR loops–
SELECT…FOR UPDATE – WHERE CURRENT OF Clause– Cursor
with Parameters– Cursor Variables– Exceptions– Types of Exceptions.
Text Book: “DATABASE SYSTEMS USING ORACLE”-NILESH SHAH,2nd Edition, PHI
Prepared by Dr.P.Radha

PL/SQL: A Programming Language
• History
• Fundamentals
• Block Structure
• Comments
• Data Types
• Other Data Types
• Variable Declaration
• Anchored Declaration
• Assignment operation
• Bind Variables
• Substitution Variables
• Printing
• Arithmetic Operators

A BRIEF HISTORY OF PL/SQL
• Before PL/SQL was developed, users
embedded SQL statements into hot languages
like C++ and Java.
• PL/SQL version 1.0 was introduced with
Oracle 6.0 in 1991.
• Version 1.0 had very limited capabilities,
however, and was far from being a full-fledged
programming language.
• It was merely used for batch processing.

Cont…
• With versions 2.0, 2.1, and 2.2, the following new features were
introduced:
• The transaction control statements SAVEPOINT, ROLLBACK, and
COMMIT.
• The DML statements INSERT, DELETE, and UPDATE.
• The extended data types Boolean, BINARY_INTEGER, PL/SQL
records, and PL/SQL tables.
• Built-in functions—character, numeric, conversion, and date
functions.
• Built-in packages.
• The control structures sequence, selection, and looping.
• Database access through work areas called cursors.
• Error handling.

Cont…
• Modular programming with procedures and
functions.
• Stored procedures, functions, and packages.
• Programmer-defined subtypes.
• DDL support through the DBMS_SQL package.
• The PL/SQL wrapper.
• The DBMS_JOB job scheduler.
• File I/O with the UTF_FILE package

FUNDAMENTALS OF PL/SQL
• A PL/SQL program consists of statements. You
may use upper- or lowercase letters in your
program.
• In other words, PL/SQL is not case sensitive
except for character string values enclosed in
single quotes.
• Like any other programming language, PL/SQL
statements consist of reserved words, identifiers,
delimiters, literals, and comments.

Cont…
Reserved Words
• The reserved words, or key words, are words
provided by the language that have a specific
use in the language.
• For example, DECLARE, BEGIN, END, IF,
WHILE, EXCEPTION, PROCEDURE,
FUNCTION, PACKAGE, and TRIGGER are
some of the reserved words in PL/SQL.

Cont…
User-Defined Identifiers
• User-defined identifiers are used to name
variables, constants, procedures, functions,
cursors, tables, records, and exceptions.
• A user must obey the following rules in
naming these identifiers:

Cont…
• The name can be from 1 to 30 characters in length.
• The name must start with a letter.
• Letters (A–Z, a–z), numbers, the dollar sign ($), the
number sign (#) and the underscore (_) are allowed.
• Spaces are not allowed.
• Other special characters are not allowed.
• Key words cannot be used as user-defined identifiers.
• Names must be unique within a block.
• A name should not be the same as the name of a
column used in the block.

Cont…
Literals
• Literals are values that are not represented by
user-defined identifiers. Literals are of three
types: Numeric, Character, and Boolean. For
example:
• Numeric100, 3.14, — 55, 5.25E7, or NULL
• Character‘A’, ‘this is a string’, ‘0001’, ‘25-
MAY-00’, ‘ ’, or NULL
• Boolean TRUE, FALSE, or NULL

PL/SQL BLOCK STRUCTURE
• PL/SQL is a block structured language. A
program can be divided into logical blocks
• The block structure gives modularity to a
PL/SQL program, and each object within a block
has “scope.” Blocks are of two types:
• An anonymous block is a block of code without a
name. It can be used anywhere in a program and
is sent to the server engine for execution at
runtime.

Cont…
• A named block is a block of code that is
named. A subprogram is a named block that
can be called and can take arguments.
• A procedure is a subprogram that can perform
an action, whereas a function is a subprogram
that returns a value.
• A package is formed from a group of
procedures and functions. A trigger is a block
that is called implicitly by a DML statement.

Cont…
A PL/SQL block consists of three sections:
• A declaration section.
• An executable section.
• An exception-handling section.

COMMENTS
• Comments are used to document programs.
They are written as part of a program, but they
are not executed.
• In fact, comments are ignored by the PL/SQL
engine.
• It is a good programming practice to add
comments to a program, because this helps in
readability and debugging of the program

Cont…
There are two ways to write comments in PL/SQL:
• To write a single-line comment, two dashes (--) are entered at the
beginning of a new line. For example,
- -This is a single-line comment.
• To write a multiline comment, comment text is placed between /*
and */. A multiline comment can be written on a separate line by
itself, or it can be used on a line of code as well. For example,
/* This is a
multiline comment
that ends here. */

DATA TYPES
Each constant and variable in the program needs
a data type. The data type decides the type of
value that can be stored in a variable. PL/SQL has
four data types:
• Scalar.
• Composite.
• Reference.
• LOB

Cont…
• A scalar data type is not made up of a group of
elements.
• It is atomic in nature.
• The composite data types are made up of
elements or components.
• PL/SQL supports three composite data
types—records, tables, and Varrays

Cont…
There are four major categories of scalar data
types:
• Character.
• Number.
• Boolean.
• Date.

OTHER DATA TYPES
NLS
The National Language Support (NLS) data
type is for character sets in which multiple
bytes are used for character representation.
NCHAR and NVARCHAR2 are examples of
NLS data types.

Cont…
LOB
• Like Oracle9i, PL/SQL also supports Large
Object (LOB) data types to store large values
of character, raw, or binary data.
• The LOB types allow up to 4 gigabytes of
data. LOB variables can be given one of the
following data types:

Cont…
• The BLOB type contains a pointer to the large
binary object inside the database.
• The CLOB type contains a pointer to a large
block of single-byte character data of fixed width.
• The NCLOB type contains a pointer to a large
block of multibyte character data of fixed width.
• The BFILE type contains a pointer to large
binary objects in an external operating system
file. It would contain the directory name and the
filename

VARIABLE DECLARATION
• A scalar variable or a constant is declared with
a data type and an initial value assignment.
The declarations are done in the DECLARE
section of the program block.
• The initial value assignment for a variable is
optional unless it has a NOT NULL constraint.
The constants and NOT NULL type variables
must be initialized.

Cont…
The general syntax is
DECLARE
identifiername [CONSTANT] datatype [NOT
NULL] [:= | DEFAULT expression];

ANCHORED DECLARATION
• PL/SQL uses %TYPE attribute to anchor a
variable’s data type. Another variable or a
column in a table can be used for anchoring
Variablename typeattribute%TYPE [value
assignment];

ASSIGNMENT OPERATION
• The assignment operation is one of the ways to
assign a value to a variable.
• You have already learned that a variable can be
initialized at the time of declaration by using
the DEFAULT option or :=.
• The assignment operation is used in the
executable section of the program block to
assign a literal, another variable’s value, or the
result of an expression to a variable.

Cont…
• The general syntax is
VariableName := Literal | VariableName |
Expression;

BIND VARIABLES
• Bind variables are also known as host
variables.
• These variables are declared in the host SQL*
Plus environment and are accessed by a
PL/SQL block.
• Anonymous blocks do not take any arguments,
but they can access host variables with a colon
prefix (:) and the host variable name.

Cont…
The syntax of a host variable declaration is
VARIABLE variablename datatype
For example,
SQL> VARIABLE double NUMBER

SUBSTITUTION VARIABLES IN PL/SQL
• PL/SQL does not have any input capabilities in
terms of having an input statement.
• There are no explicit input/output (I/O)
statements, but substitution variables of SQL
are available in PL/SQL.
• Substitution variables have limitations, which
become apparent in a loop.

PRINTING IN PL/SQL
• There is no explicit output statement in
PL/SQL. Oracle does have a built-in package
called DBMS_OUTPUT with the procedure
PUT_LINE to print.
• An environment variable named
SERVEROUTPUT must be toggled ON to
view output from it.

Cont…
• The DBMS_OUTPUT is the most frequently used
package because of its capabilities to get lines
from a file and to put lines into the buffer.
• The PUT_LINE procedure displays information
passed to the buffer and puts a new-line marker at
the end.
For example,
DBMS_OUTPUT.PUT_LINE (‘This line will be
displayed’);

ARITHMETIC OPERATORS
• Five standard arithmetic operators are
available in PL/SQL for calculations.
• If more than one operator exists in an
arithmetic expression, the following order of
precedence is used:

Cont…
• Exponentiation is performed first,
multiplication and division are performed next,
and addition and subtraction are performed
last.
• If more than one operator of the same priority
is present, they are performed from left to
right.
• Whatever is in parentheses is performed first.

Cont…
Arithmetic Operator Use
+ Addition
- Subtraction
/ Division
* Multiplication
** Exponentiation

Control Structures and Embedded SQL:
• Control Structures
• Nested Blocks
• SQL in PL/SQL
• Data Manipulation
• Transaction Control statements.

CONTROL STRUCTURES
• In a procedural language like PL/SQL, there
are three basic programming control
structures:
• In a sequential structure, a series of
instructions are performed from the beginning
to the end in a linear order. None of the
instructions is skipped, and none of the
instructions is repeated.

Cont..
• The selection structure is also known as a
decision structure or an IF- structure.
• It involves conditions with a TRUE or FALSE
outcome.
• Based on the outcome, one of the options is
performed, and the other option is skipped.
Selection statements are also available for
multiple options.

Cont..
• In a looping structure, a series of instructions
is performed repeatedly.
• There are different looping statements
appropriate for a variety of situations.
• A programmer has to write a loop correctly to
make it perform a specific number of times.

Cont..
Selection Structure
• There are three selection or conditional
statements in PL/SQL.
• Relational operators, logical operators, and
other special operators are used to create
Boolean expressions or conditions

Cont..
• The AND and OR operators are binary
operators, because they work on two
conditions.
• The NOT operator is a unary operator,
because it works on a single condition.

Cont..
Nested IF.
• The nested IF statement contains an IF statement within
another IF statement. If the condition in the outer IF
statement is TRUE, the inner IF statement is performed.
Any IF statement with a compound condition can be written
as a nested IF statement. For example, the program segment
in Figure 11-12 assigns an insurance surcharge based on an
individual’s gender and age. There are four categories:
• Male 25 or over.
• Male under 25.
• Female 25 or over.
• Female under 25.

Cont…
Looping Structure
• Looping means iterations. A loop repeats a
statement or a series of statements a specific
number of times, as defined by the programmer.
• Three types of looping statements are available in
PL/SQL:
• Basic loop.
• WHILE loop.
• FOR loop.

Cont…
Basic loop
• A basic loop is a loop that is performed
repeatedly. Once a loop is entered, all statements
in the loop are performed.
• When the bottom of the loop is reached, control
shifts back to the top of the loop. The loop will
continue in- finitely.
• An infinite loop, or a “never-ending loop,” is a
logical error in programming.
• The only way to terminate a basic loop is by
adding an EXIT statement inside the loop.

Cont…
LOOP
Looping statement1; Looping statement2;
. . .
Looping statementN; EXIT [WHEN condition];
END LOOP;

Cont…
WHILE loop
• The WHILE loop is an alternative to the basic
loop and is performed as long as the
condition is true. It terminates when the
condition becomes false. If the condition is
false at the beginning of the loop, the loop is
not performed at all.
• The WHILE loop does not need an EXIT
statement to terminate.

Cont..
WHILE condition
LOOP Looping statement1;
Looping statement2;
...
Looping statement n;
END LOOP;

Cont…
FOR loop
• The FOR loop is the simplest loop you can
write. Unlike the basic and WHILE loops, you
do not have to initialize, test, and
increment/decrement the loop control variable
separately

Cont…
FOR counter IN [REVERSE] lower..upper LOOP
Looping statement1
Looping statement2
.. .
Looping statementN
END LOOP;

Cont..
Nested loops
• Loops can be nested to many levels. When the
inner loop ends, it does not automatically end
the outer loop enclosing it.
• The loop labels use the same naming rules as
those used for identifiers. The loops are
labeled before the key word LOOP on the
same line or on a separate line.

NESTED BLOCKS
• PL/SQL block may contain another PL/SQL
block; in other words, PL/SQL blocks can be
nested.
• The execution starts with the outer block and
continues with the inner block.
• The variables declared in the outer block are
global to the inner block, and they are accessible
in the inner block.
• The variables declared in the inner block,
however, are not accessible in the outer block.

SQL IN PL/ SQL
• The PL/SQL statements have control structures
for calculations, decision making, and iterations
• PL/SQL does not support Data Definition
Language (DDL) statements, such as CREATE,
ALTER, and DROP.
• The Data Control Language (DCL) statements
GRANT and REVOKE also are not available in
PL/SQL.

DATA MANIPULATION IN PL/SQL
The three DML statements to manipulate data
are:
• The INSERT statement to add a new row in a
table.
• The DELETE statement to remove a row or
rows.
• The UPDATE statement to change values in a
row or rows.

TRANSACTION CONTROL STATEMENTS
• The COMMIT statement to commit the current
transaction.
• The SAVEPOINT statement to mark a point in
your transaction.
• The ROLLBACK [TO SAVEPOINT n]
statement to discard all or part of the
transaction.

PL/SQL Cursors and Exceptions
• Cursors
• Implicit & Explicit Cursors and Attributes
• Cursor FOR loops
• SELECT…FOR UPDATE
• WHERE CURRENT OF clause
• Cursor with Parameters
• Cursor Variables
• Exceptions
• Types of Exceptions

Cursors
• When you execute an SQL statement from a
PL/SQL block, Oracle assigns a private work
area for that statement.
• The work area, called a cursor, stores the
statement and the results returned by execution
of that statement.
• A cursor is created either implicitly or
explicitly by you.

Cont…
Types of Cursors
• In a static cursor, the contents are known at
compile time. The cursor object for such an
SQL statement is always based on one SQL
statement.
• In a dynamic cursor, a cursor variable that can
change its value is used. The variable can refer
to different SQL statements at different times.

IMPLICIT CURSORS
• PL/SQL creates an implicit cursor when an SQL
statement is executed from within the program
block.
• The implicit cursor is created only if an explicit
cursor is not attached to that SQL statement.
Oracle opens an implicit cursor, and the pointer is
set to the first (and the only) row in the cursor.
Then, the SQL statement is fetched and executed
by the SQL engine on the Oracle server

EXPLICIT CURSORS
• An explicit cursor is declared as a SELECT
statement in the PL/SQL block. It is given a
name, and you can use explicit statements to
work with it.
• You have total control of when to open the
cursor, when to fetch a row from it, and when
to close it.
• There are cursor attributes in PL/SQL to get
the status information on explicit cursors.

Cont…
Four actions can be performed on an explicit
cursor:
• Declare it.
• Open it.
• Fetch row(s) from it.
• Close it.

Cont..
Declaring an Explicit Cursor
• A cursor is declared as a SELECT statement. The SELECT
statement must not have an INTO clause in a cursor’s declaration.
• If you want to retrieve rows in a specific order into a cursor, an
ORDER BY clause can be used in the SELECT statement.
DECLARE
CURSOR cursorname IS
SELECT statement;

Cont…
Opening a Cursor
• When a cursor is opened, its SELECT query is executed.
• The active set is created using all tables in the query and then
restricting to rows that meet the criteria.
• The data retrieved by the SELECT query is brought into the
cursor or the work area.
• The cursor points to the first row in the active set. PL/SQL
uses an OPEN statement to open a cursor.
OPEN cursorname;

Cont..
Fetching Data from a Cursor
• The SELECT statement creates an active set
based on tables in the FROM clause, column
names in the SELECT clause, and rows based on
conditions in the WHERE clause.
• The number of variables must match the number
of columns in the row. In PL/SQL, a FETCH
statement is used for this action.
FETCH cursorname INTO variablelist / recordname;

Cont…
Closing a cursor
• When you are done with a cursor, you should close it.
• A closed cursor can be reopened again. If you terminate
your PL/SQL program without closing an open cursor,
it will not result in an exception.
• A user releases memory by closing a cursor.
• PL/SQL uses the CLOSE statement to close a cursor.
CLOSE cursorname;

EXPLICIT CURSOR ATTRIBUTES
Actions can be performed on cursors with OPEN, FETCH, and CLOSE
statements. The four explicit cursor attributes are:
%ISOPEN It returns TRUE if the cursor is open;
otherwise, it returns FALSE.
%FOUND It returns TRUE if the last fetch returned a row; other-
wise, it returns FALSE.
%NOTFOUND It returns TRUE if the last fetch did not return a row;
otherwise, it returns FALSE. It complements the
%FOUND attribute.
%ROWCOUND It returns total number of rows returned.

IMPLICIT CURSOR ATTRIBUTES
• An implicit cursor cannot be opened, fetched
from, or closed with a statement. You do not
name implicit cursors.
• The cursor attributes are available for an
implicit cursor with the name SQL as a prefix.

Cont..
The four attributes for a implicit cursor are:
• SQL%ISOPEN.
• SQL%ROWCOUNT.
• SQL%NOTFOUND.
• SQL%FOUND.

CURSOR FOR LOOPS
• The cursor FOR loop is the easiest way to
write a loop for explicit cursors. The cursor is
opened implicitly when the loop starts.
• A row is then fetched into the record from
the cursor with every iteration of the loop.
• The cursor is closed automatically when the
loop ends, and the loop ends when there are no
more rows

Cont…
FOR recordname IN cursorname LOOP
Loop statements;
. . .
END LOOP;

Cont…
Cursor FOR Loop Using a Subquery
• Use of a subquery in the cursor FOR loop
eliminates declaration of an explicit cursor.
• The cursor is created by a subquery in the
FOR loop statement itself.

SELECT . . . FOR UPDATE CURSOR
• When you type a SELECT query, the result is
returned to you without locking any rows in
the table.
• Row locking is kept to a minimum. You can
explicitly lock rows for update before
changing them in the program.
• The FOR UPDATE clause is used with the
SELECT query for row locking.

Cont…
• The locked rows are not available to other users for DML
statements until you release them with COMMIT or
ROLLBACK commands.
• Rows that are locked for update do not have to be updated.
CURSOR cursorname IS
SELECT columnnames
FROM tablename(s) [WHERE condition]
FOR UPDATE [OF columnnames] [NOWAIT];

WHERE CURRENT OF CLAUSE
• In a cursor, data manipulation in the form of UPDATE
or DELETE is performed on rows fetched. The
WHERE CURRENT OF clause allows you to perform
data manipulation only on a recently fetched row.
UPDATE tablename SET clause
WHERE CURRENT OF cursorname;
DELETE FROM tablename
WHERE CURRENT OF cursorname;

CURSOR WITH PARAMETERS
• A cursor can be declared with parameters,
which allow you to pass values to the cursor.
• These values are passed to the cursor when it
is opened, and they are used in the query when
it is executed.
• With the use of parameters, you can open and
close a cursor many times with different
values.

Cont…
• When parameters are passed, you need not
worry about the scope of variables.
CURSOR cursorname
[(parameter1 datatype, parameter2 datatype, )]
IS
SELECT query;

CURSOR VARIABLES: AN INTRODUCTION
• An explicit cursor is the name of the work area
for an active set.
• A cursor variable is a reference to the work
area.
• A cursor is based on one specific query,
whereas a cursor variable can be opened with
different queries within a program.
• A static cursor is like a constant, and a cursor
variable is like a pointer to that cursor.

Cont…
REF CURSOR Type
• Two steps are involved in creating a cursor variable. First,
you have to create a referenced cursor type.
• Second, you have to declare an actual cursor variable with
the referenced cursor type.
TYPE cursortypename IS REF CURSOR [RETURN
returntype];
cursorvarname cursortypename;

Cont…
Opening a Cursor Variable
You assign a cursor to the cursor variable when
you OPEN it.
• OPEN cursorname / cursorvarname FOR
SELECT query;

Cont…
Fetching from a Cursor Variable
• The fetching action is same as that of a cursor.
The compiler checks the data structure type
after the INTO clause to see if it matches the
query linked to the cursor.
FETCH cursorvarname INTO recordname /
variablelist;

EXCEPTIONS
• An exception occurs when an unwanted
situation arises during the execution of a
program.
• Exceptions can result from a system error, a
user error, or an application error.
• When an exception occurs, control of the
current program block shifts to another section
of the program, known as the exception
section, to handle exceptions.

TYPES OF EXCEPTIONS
There are three types of exceptions in PL/SQL:
• Predefined Oracle server exceptions are
exceptions that are named by PL/SQL and are
raised implicitly when a PL/SQL or DBMS error
occurs.
• Non-predefined Oracle server exceptions are
standard Oracle server errors that are not named
by the system. They can be declared in the decla-
ration section but are raised implicitly by the
server. These exceptions do not have a name, but
they do have an associated error number.

Cont…
3. User-defined exceptions are exceptions that
are declared in the declaration section and are
raised by the user explicitly.
• The user decides which abnormal condition is
an exception.
• The Oracle server does not consider these
conditions to be errors.

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