PLSQL Presentation

7/29/2019 PLSQL Presentation

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PL/SQL


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PL/SQL Block Structure

DECLARE (optional)

BEGIN (required)

EXCEPTION (optional)

END; (required)


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Comments in PL/SQL Block

Single Line(-- Comment)

Multi Line(/* Comment */)


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PL/SQL Block Types

Anonymous

DECLAREBEGIN

-statements

EXCEPTION

END;

Procedure

PROCEDURE(param1,2..)

IS

BEGIN

-statements

EXCEPTIONEND;

Function

FUNCTION>(param1,2

..)

RETURN

IS

BEGIN-statements

EXCEPTION

END;


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PL/SQL placeholders

All SQL types are supported by PL/SQL Numerical types

NUMBER, PLS_INTEGER

Many derived types, e.g. POSITIVE

Character types

CHAR, VARCHAR2, NCHAR,

Other scalar types

BOOLEAN, DATE


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PL/SQL placeholders

Scalar type

variable

constant

Composite/vector type

record - used for reading rows from table


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PL/SQL placeholders

Scalar type

variable

Constant

DECLAREl_x NUMBER := 20000;

l_message VARCHAR2(40);

C_PI CONSTANT NUMBER(3,2):=3.14;

BEGIN

l_x := 1000 * C_PI;

l_message := 'Hello world';

END;


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Attributes %TYPE and %ROWTYPE

%TYPE references type of a variable or a

database column

%ROWTYPE references type of a record

structure, table row or a cursor

Advantage: an actual type does not need to be known


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%TYPE and %ROWTYPE examples

balance NUMBER(7,2);

minimum_balance balance%TYPE := 10.00;

my_dname dept.dname%TYPE;

dept_rec dept%ROWTYPE;

SELECT deptno, dname, loc INTO dept_rec

FROM dept WHERE deptno = 30;


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User-Defined Records

Defining a Record

TYPE

type_name IS RECORD

( field_name1 datatype1 ,field_name2 datatype2 );

record-name type_name;

DECLARE

TYPE books IS RECORD

( title varchar(50),

author varchar(50),subject varchar(100),

book_id number);

book1 books;

book2 books;


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PL/SQL Control Structures

Conditional Control Using IF and CASE statements


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Example

DECLARE

l_sales NUMBER(8,2) := 20000;

l_bonus NUMBER(6,2);

BEGIN

IF l_sales > 50000 THEN l_bonus :=

1500;

ELSIFl_sales > 35000 THENl_bonus :=

500;ELSEl_bonus := 100;

END IF;

UPDATE employees SET salary = salary +

l_bonus;

END;

DECLARE

l_grade CHAR(1) := 'B';

BEGIN

CASEl_grade

WHEN'A' THEN

DBMS_OUTPUT.PUT_LINE('Excellent');

WHEN'B' THEN

DBMS_OUTPUT.PUT_LINE('Very Good');

WHEN'C' THEN

DBMS_OUTPUT.PUT_LINE('Good');

WHEN'D' THEN

DBMS_OUTPUT.PUT_LINE('Fair');

WHEN'F' THEN

DBMS_OUTPUT.PUT_LINE('Poor');

ELSEDBMS_OUTPUT.PUT_LINE('No

such grade');

END CASE;

END;


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PL/SQL Control Structures

Iterative loops Simple loop (infinite)

WHILE loop

FOR loop

Numeric range

Reversed

Cursor based

DECLARE

l_i NUMBER := 0;

BEGIN

LOOP

DBMS_OUTPUT.PUT_LINE(TO_CHAR(l_i));

l_i:=l_i+1;

END LOOP;

WHILEl_i < 10 LOOP

DBMS_OUTPUT.PUT_LINE (TO_CHAR(l_i));

l_i := l_i + 1;

END LOOP;

FORl_i IN 1..500 LOOP

DBMS_OUTPUT.PUT_LINE (TO_CHAR(l_i));

END LOOP;

FORl_i INREVERSE1..3 LOOPDBMS_OUTPUT.PUT_LINE (TO_CHAR(l_i));

END LOOP;

END;

P i P d d


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Parameters in Procedure and

Functions

In PL/SQL, we can pass parameters to procedures andfunctions in three ways.

1) IN type parameter: These types of parameters are usedto send values to stored procedures.2) OUT type parameter: These types of parameters areused to get values from stored procedures. This is similar toa return type in functions.3) IN OUT parameter: These types of parameters are usedto send values and get values from stored procedures.

NOTE: If a parameter is not explicitly defined a parametertype, then by default it is an IN type parameter.


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Example

DECLARE

a number;

b number;

c number;

PROCEDURE findSum(x IN number, y IN number, z IN OUT number)

IS

BEGIN

z:=x+y;

END IF;

END;

BEGIN

a:= 23;

b:= 45;

findSum (a, b, c);

dbms_output.put_line(' Sum of (23, 45) : ' || c);

END;


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Cursors


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What are Cursors?

A cursor is a temporary work area created in the

system memory when a SQL statement is

executed. A cursor contains information on a

select statement and the rows of data accessedby it.

There are two types of cursors in PL/SQL:

Implicit cursors

Explicit cursors


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Implicit Cursors

Automatically created and destroyed by

Oracle.

Outcome of the statement can be determined

by using

SQL%ATTRIBUTE_NAME

Some attributes are explained on the next

slide.


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Example

DECLARE var_rows number(5);

BEGIN

UPDATE employee

SET salary = salary + 1000;

IF SQL%NOTFOUND THEN

dbms_output.put_line('None of the salaries where updated');

ELSIF SQL%FOUND THEN

var_rows := SQL%ROWCOUNT;

dbms_output.put_line('Salaries for ' || var_rows || 'employees areupdated');

END IF;

END;


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Explicit Cursors

An explicit cursor is defined in the declaration sectionof the PL/SQL Block.

General Syntax for creating a cursor is as given below:

CURSOR cursor_name IS select_statement;

cursor_name A suitable name for the cursor.

select_statementA select query which returnsmultiple rows.


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How to use Explicit Cursor?

There are four steps in using an Explicit Cursor.

DECLARE the cursor in the declaration section.

OPEN the cursor in the Execution Section. FETCH the data from cursor into PL/SQL

variables or records in the Execution Section.

CLOSE the cursor in the Execution Sectionbefore you end the PL/SQL Block.


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Declaration

DECLARE

CURSOR emp_cur IS

SELECT *FROM emp_tbl

WHERE salary > 5000;


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How to access an Explicit Cursor?

These are the three steps in accessing the cursor.1) Open the cursor.

OPEN cursor_name;

2) Fetch the records in the cursor one at a time.FETCH cursor_name INTO record_name;

ORFETCH cursor_name INTO variable_list;

3) Close the cursor.

CLOSE cursor_name;


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Cursor with a Simple Loop

DECLARE

CURSOR emp_cur IS

SELECT first_name, last_name, salary FROM emp_tbl;

emp_rec emp_cur %rowtype;

BEGIN

IF NOT sales_cur%ISOPEN THEN

OPEN sales_cur;

END IF;

LOOP

FETCH emp_cur INTO emp_rec;

EXIT WHEN emp_cur%NOTFOUND;

dbms_output.put_line(emp_cur.first_name || ' ' ||emp_cur.last_name|| ' ' ||emp_cur.salary);

END LOOP;

END;


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Cursor with a While Loop

DECLARE

CURSOR emp_cur IS


emp_rec emp_cur%rowtype;

BEGIN

IF NOT sales_cur%ISOPEN THEN

OPEN sales_cur;

END IF;

FETCH sales_cur INTO sales_rec;

WHILE sales_cur%FOUND THEN

LOOP

dbms_output.put_line(emp_cur.first_name || ' ' ||emp_cur.last_name|| ' ' ||emp_cur.salary);

FETCH sales_cur INTO sales_rec;

END LOOP;

END;


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Cursor with a FOR Loop

DECLARE

CURSOR emp_cur IS


BEGIN

FOR emp_rec in c1

LOOP

dbms_output.put_line(emp_cur.first_name || ' ' ||emp_cur.last_name

|| ' ' ||emp_cur.salary);

END LOOP;

END;


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Parameterized Cursor

DECLARE

cursor c(no number) is select * from emp_information

where emp_no = no;

tmp emp_information%rowtype;

BEGIN

FOR tmp IN c(4) LOOP

dbms_output.put_line('EMP_No: '||tmp.emp_no);

dbms_output.put_line('EMP_Name: '||tmp.emp_name);

dbms_output.put_line('EMP_Dept: '||tmp.emp_dept);

dbms_output.put_line('EMP_Salary:'||tmp.emp_salary);

END LOOP;

END;


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Exception Handling


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Exception Handling

PL/SQL Exception message consists of three

parts.

1) Type of Exception

2) An Error Code3) A message


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Structure of Exception Handling

DECLARE

Declaration section

BEGIN

Exception section

EXCEPTION

WHEN ex_name1 THEN

-Error handling statements

WHEN ex_name2 THEN

-Error handling statements

WHEN Others THEN-Error handling statements

END;


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Types of Exception

There are 3 types of Exceptions.

a) Named System Exceptions

b) Unnamed System Exceptions

c) User-defined Exceptions


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a) Named System Exceptions

System exceptions are automatically raised by Oracle.

There are some system exceptions which are raisedfrequently, so they are pre-defined and given a name inOracle which are known as Named System Exception.

E.g.:

BEGIN

Execution section

EXCEPTION

WHEN NO_DATA_FOUND THEN

dbms_output.put_line ('A SELECT...INTO did not return anyrow.');

END;


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Example


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Unnamed System Exceptions

The system exception for which oracle does

not provide a name is known as unnamed

system exception.

These exception do not occur frequently.

These Exceptions have a code and an

associated message.


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Syntax

DECLARE

exception_name EXCEPTION;

PRAGMA

EXCEPTION_INIT (exception_name, Err_code);

BEGIN

Execution section

EXCEPTION

WHEN exception_name THEN

handle the exception

END;


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Example

Example: Lets consider the product table and order_items table.

Here product_id is a primary key in product table and a foreign key in order_items table.

If we try to delete a product_id from the product table when it has child records in order_id

table an exception will be thrown with oracle code number -2292.

We can provide a name to this exception and handle it in the exception section as given

below.

DECLARE

Child_rec_exception EXCEPTION;

PRAGMA

EXCEPTION_INIT (Child_rec_exception, -2292);

BEGINDelete FROM product where product_id= 104;

EXCEPTION

WHEN Child_rec_exception

THEN Dbms_output.put_line('Child records are present for this product_id.');

END;


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User-defined Exceptions

Apart from system exceptions we can explicitlydefine exceptions based on business rules.

Steps to be followed to use user-defined

exceptions: They should be explicitly declared in thedeclaration section. They should be explicitly raised in the Execution

Section. They should be handled by referencing the user-defined exception name in the exception section.


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Example

DECLARE

c_id customers.id%type := &cc_id;

c_name customers.name%type;

c_addr customers.address%type;

ex_invalid_id EXCEPTION;

BEGIN

IF c_id


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RAISE_APPLICATION_ERROR ( )

RAISE_APPLICATION_ERROR is a built-in procedure inoracle which is used to display the user-defined errormessages along with the error number whose range is inbetween -20000 and -20999.

RAISE_APPLICATION_ERROR raises an exception butdoes not handle it.

RAISE_APPLICATION_ERROR is used for the followingreasons,

a) to create a unique id for an user-defined exception.b) to make the user-defined exception look like anOracle error.


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Syntax

RAISE_APPLICATION_ERROR (error_number,error_message); The Error number must be between -20000 and -20999 The Error_message is the message you want to displaywhen the error occurs.

Steps to be folowed to use RAISE_APPLICATION_ERRORprocedure:1. Declare a user-defined exception in the declarationsection.2. Raise the user-defined exception based on a specific

business rule in the execution section.3. Finally, catch the exception and link the exception to auser-defined error number in RAISE_APPLICATION_ERROR.


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Example

CREATE OR REPLACE PROCEDURE Register is

BEGIN

RAISE_APPLICATION_ERROR(-20000, 'Can''t add more Employee');

EXCEPTIONWHEN NO_DATA_FOUND THEN

RAISE_APPLICATION_ERROR(20001, ' doesn''t exist!');

END Register;


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SQLCODE and SQLERRM

SQLCODE: It returns the error number for the error.SQLERRM: It returns the actual error message ofthe error.

When a SQL statement raises an exception,Oracle captures the error codes by using theSQLCODE and SQLERRM globally-definedvariables.

SQLCODE and SQLERRM can track exceptions thatare handled by the OTHERS clause of theexception handler.


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Example

Declarev_sal1 emp.empno%Type := &sal1;v_ename1 emp.ename%Type;

Begin

Select ename into v_ename1

From emp Where sal=v_sal1;dbms_output.put_line('Name: '||v_ename1);

ExceptionWhen no_data_found then

dbms_output.put_line('Employee not found with '||v_sal1);When others then

dbms_output.put_line('The program received an error. Errormessage returned was: ' || SQLCODE || ',' || SQLERRM);

End;


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Triggers

A trigger is a pl/sql block structure which is

fired when a DML statements like Insert,

Delete, Update is executed on a database

table.

A trigger is triggered automatically when an

associated DML statement is executed.


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Syntax

CREATE [OR REPLACE ] TRIGGER trigger_name{BEFORE | AFTER }

{INSERT [OR] | UPDATE [OR] | DELETE}

[OF col_name]

ON table_name[REFERENCING OLD AS o NEW AS n]

[FOR EACH ROW]

WHEN (condition)

BEGIN--- sql statements

END;


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Example

CREATE OR REPLACE TRIGGER audit_sal

BEFORE UPDATE OF salary ON employees

FOR EACH ROW

BEGIN

INSERT INTO emp_audit

VALUES( :old.employee_id, SYSDATE, :new.salary, :old.salary );

COMMIT;

END;


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Q & A


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Thank You

Date post:	14-Apr-2018
Category:	Documents
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