PL/SQl cursors

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 accessed by it. This temporary work area is used to store the data retrieved from the database, and manipulate this data. A cursor can hold more than one row, but can process only one row at a time. The set of rows the cursor holds is called the active set.

There are two types of cursors in PL/SQL:
Implicit cursors:
These are created by default when DML statements like, INSERT, UPDATE, and DELETE statements are executed. They are also created when a SELECT statement that returns just one row is executed.


Explicit cursors:

They must be created when you are executing a SELECT statement that returns more than one row. Even though the cursor stores multiple records, only one record can be processed at a time, which is called as current row. When you fetch a row the current row position moves to next row.
Both implicit and explicit cursors have the same functionality, but they differ in the way they are accessed.



Implicit Cursors:

When you execute DML statements like DELETE, INSERT, UPDATE and SELECT statements, implicit statements are created to process these statements.

Oracle provides few attributes called as implicit cursor attributes to check the status of DML operations. The cursor attributes available are %FOUND, %NOTFOUND, %ROWCOUNT, and %ISOPEN.

For example, When you execute INSERT, UPDATE, or DELETE statements the cursor attributes tell us whether any rows are affected and how many have been affected.
When a SELECT... INTO statement is executed in a PL/SQL Block, implicit cursor attributes can be used to find out whether any row has been returned by the SELECT statement. PL/SQL returns an error when no data is selected.

The status of the cursor for each of these attributes are defined in the below table.
Attributes
   

Return Value
   

Example

%FOUND
   

The return value is TRUE, if the DML statements like INSERT, DELETE and UPDATE affect at least one row and if SELECT ….INTO statement return at least one row.
   

SQL%FOUND

The return value is FALSE, if DML statements like INSERT, DELETE and UPDATE do not affect row and if SELECT….INTO statement do not return a row.

%NOTFOUND
   

The return value is FALSE, if DML statements like INSERT, DELETE and UPDATE at least one row and if SELECT ….INTO statement return at least one row.
   

SQL%NOTFOUND

The return value is TRUE, if a DML statement like INSERT, DELETE and UPDATE do not affect even one row and if SELECT ….INTO statement does not return a row.

%ROWCOUNT
   

Return the number of rows affected by the DML operations INSERT, DELETE, UPDATE, SELECT
   

SQL%ROWCOUNT

For Example: Consider the PL/SQL Block that uses implicit cursor attributes as shown below:

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 are updated');

  END IF;

END;

In the above PL/SQL Block, the salaries of all the employees in the ‘employee’ table are updated. If none of the employee’s salary are updated we get a message 'None of the salaries where updated'. Else we get a message like for example, 'Salaries for 1000 employees are updated' if there are 1000 rows in ‘employee’ table.

PL/SQL iterative

Iterative Statements in PL/SQL

An iterative control Statements are used when we want to repeat the execution of one or more statements for specified number of times. These are similar to those in

There are three types of loops in PL/SQL:
• Simple Loop
• While Loop
• For Loop
1) Simple Loop

A Simple Loop is used when a set of statements is to be executed at least once before the loop terminates. An EXIT condition must be specified in the loop, otherwise the loop will get into an infinite number of iterations. When the EXIT condition is satisfied the process exits from the loop.
The General Syntax to write a Simple Loop is:

LOOP

   statements;

   EXIT;

   {or EXIT WHEN condition;}

END LOOP;
These are the important steps to be followed while using Simple Loop.

1) Initialise a variable before the loop body.
2) Increment the variable in the loop.
3) Use a EXIT WHEN statement to exit from the Loop. If you use a EXIT statement without WHEN condition, the statements in the loop is executed only once.
2) While Loop

A WHILE LOOP is used when a set of statements has to be executed as long as a condition is true. The condition is evaluated at the beginning of each iteration. The iteration continues until the condition becomes false.
The General Syntax to write a WHILE LOOP is:

WHILE <condition>

 LOOP statements;

END LOOP;
Important steps to follow when executing a while loop:

1) Initialise a variable before the loop body.
2) Increment the variable in the loop.
3) EXIT WHEN statement and EXIT statements can be used in while loops but it's not done oftenly.
3) FOR Loop

A FOR LOOP is used to execute a set of statements for a predetermined number of times. Iteration occurs between the start and end integer values given. The counter is always incremented by 1. The loop exits when the counter reachs the value of the end integer.

The General Syntax to write a FOR LOOP is:

FOR counter IN val1..val2

  LOOP statements;

END LOOP;

    val1 - Start integer value.
    val2 - End integer value.
Important steps to follow when executing a while loop:

1) The counter variable is implicitly declared in the declaration section, so it's not necessary to declare it explicity.
2) The counter variable is incremented by 1 and does not need to be incremented explicitly.
3) EXIT WHEN statement and EXIT statements can be used in FOR loops but it's not done oftenly.

NOTE: The above Loops are explained with a example when dealing with Explicit Cursors.

PL/SQL exceptions

Exception Handling

In this section we will discuss about the following,
1) What is Exception Handling.
2) Structure of Exception Handling.
3) Types of Exception Handling.

1) What is Exception Handling?

PL/SQL provides a feature to handle the Exceptions which occur in a PL/SQL Block known as exception Handling. Using Exception Handling we can test the code and avoid it from exiting abruptly. When an exception occurs a messages which explains its cause is recieved.
PL/SQL Exception message consists of three parts.
1) Type of Exception
2) An Error Code
3) A message
By Handling the exceptions we can ensure a PL/SQL block does not exit abruptly.

2) Structure of Exception Handling.

The General Syntax for coding the exception section

 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; 

General PL/SQL statments can be used in the Exception Block.
When an exception is raised, Oracle searches for an appropriate exception handler in the exception section. For example in the above example, if the error raised is 'ex_name1 ', then the error is handled according to the statements under it. Since, it is not possible to determine all the possible runtime errors during testing fo the code, the 'WHEN Others' exception is used to manage the exceptions that are not explicitly handled. Only one exception can be raised in a Block and the control does not return to the Execution Section after the error is handled.
If there are nested PL/SQL blocks like this.

 DELCARE

   Declaration section 

 BEGIN

    DECLARE

      Declaration section 

    BEGIN 

      Execution section 

    EXCEPTION 

      Exception section 

    END; 

 EXCEPTION

   Exception section 

 END; 

In the above case, if the exception is raised in the inner block it should be handled in the exception block of the inner PL/SQL block else the control moves to the Exception block of the next upper PL/SQL Block. If none of the blocks handle the exception the program ends abruptly with an error.

3) Types of Exception.

There are 3 types of Exceptions.
a) Named System Exceptions
b) Unnamed System Exceptions
c) User-defined Exceptions

a) Named System Exceptions

System exceptions are automatically raised by Oracle, when a program violates a RDBMS rule. There are some system exceptions which are raised frequently, so they are pre-defined and given a name in Oracle which are known as Named System Exceptions.
For example: NO_DATA_FOUND and ZERO_DIVIDE are called Named System exceptions.
Named system exceptions are:
1) Not Declared explicitly,
2) Raised implicitly when a predefined Oracle error occurs,
3) caught by referencing the standard name within an exception-handling routine.

Exception Name	Reason	Error Number
CURSOR_ALREADY_OPEN	When you open a cursor that is already open.	ORA-06511
INVALID_CURSOR	When you perform an invalid operation on a cursor like closing a cursor, fetch data from a cursor that is not opened.	ORA-01001
NO_DATA_FOUND	When a SELECT...INTO clause does not return any row from a table.	ORA-01403
TOO_MANY_ROWS	When you SELECT or fetch more than one row into a record or variable.	ORA-01422
ZERO_DIVIDE	When you attempt to divide a number by zero.	ORA-01476

For Example: Suppose a NO_DATA_FOUND exception is raised in a proc, we can write a code to handle the exception as given below.

BEGIN 

  Execution section

EXCEPTION 

WHEN NO_DATA_FOUND THEN 

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

 END; 

b) Unnamed System Exceptions

Those system exception for which oracle does not provide a name is known as unamed system exception. These exception do not occur frequently. These Exceptions have a code and an associated message.
There are two ways to handle unnamed sysyem exceptions:
1. By using the WHEN OTHERS exception handler, or
2. By associating the exception code to a name and using it as a named exception.
We can assign a name to unnamed system exceptions using a Pragma called EXCEPTION_INIT.
EXCEPTION_INIT will associate a predefined Oracle error number to a programmer_defined exception name.
Steps to be followed to use unnamed system exceptions are
• They are raised implicitly.
• If they are not handled in WHEN Others they must be handled explicity.
• To handle the exception explicity, they must be declared using Pragma EXCEPTION_INIT as given above and handled referecing the user-defined exception name in the exception section.
The general syntax to declare unnamed system exception using EXCEPTION_INIT is:

DECLARE 

   exception_name EXCEPTION; 

   PRAGMA 

   EXCEPTION_INIT (exception_name, Err_code); 

BEGIN 

Execution section

EXCEPTION

  WHEN exception_name THEN

     handle the exception

END;

For Example: Lets consider the product table and order_items table from sql joins.
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); 

BEGIN 

  Delete 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; 

/ 

c) User-defined Exceptions

Apart from sytem exceptions we can explicity define exceptions based on business rules. These are known as user-defined exceptions.
Steps to be followed to use user-defined exceptions:
• They should be explicitly declared in the declaration 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.
For Example: Lets consider the product table and order_items table from sql joins to explain user-defined exception.
Lets create a business rule that if the total no of units of any particular product sold is more than 20, then it is a huge quantity and a special discount should be provided.

DECLARE 

  huge_quantity EXCEPTION; 

  CURSOR product_quantity is 

  SELECT p.product_name as name, sum(o.total_units) as units

  FROM order_tems o, product p

  WHERE o.product_id = p.product_id; 

  quantity order_tems.total_units%type; 

  up_limit CONSTANT order_tems.total_units%type := 20; 

  message VARCHAR2(50); 

BEGIN 

  FOR product_rec in product_quantity LOOP 

    quantity := product_rec.units;

     IF quantity > up_limit THEN 

      message := 'The number of units of product ' || product_rec.name ||  

                 ' is more than 20. Special discounts should be provided. 

   Rest of the records are skipped. '

     RAISE huge_quantity; 

     ELSIF quantity < up_limit THEN 

      v_message:= 'The number of unit is below the discount limit.'; 

     END IF; 

     dbms_output.put_line (message); 

  END LOOP; 

 EXCEPTION 

   WHEN huge_quantity THEN 

     dbms_output.put_line (message); 

 END; 

/ 

RAISE_APPLICATION_ERROR ( )

RAISE_APPLICATION_ERROR is a built-in procedure in oracle which is used to display the user-defined error messages along with the error number whose range is in between -20000 and -20999.
Whenever a message is displayed using RAISE_APPLICATION_ERROR, all previous transactions which are not committed within the PL/SQL Block are rolled back automatically (i.e. change due to INSERT, UPDATE, or DELETE statements).
RAISE_APPLICATION_ERROR raises an exception but does not handle it.
RAISE_APPLICATION_ERROR is used for the following reasons,
a) to create a unique id for an user-defined exception.
b) to make the user-defined exception look like an Oracle error.
The General Syntax to use this procedure is:

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 display when the error occurs. Steps to be folowed to use RAISE_APPLICATION_ERROR procedure:
1. Declare a user-defined exception in the declaration section.
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 a user-defined error number in RAISE_APPLICATION_ERROR.
Using the above example we can display a error message using RAISE_APPLICATION_ERROR.

DECLARE

  huge_quantity EXCEPTION; 

  CURSOR product_quantity is 

  SELECT p.product_name as name, sum(o.total_units) as units

  FROM order_tems o, product p

  WHERE o.product_id = p.product_id; 

  quantity order_tems.total_units%type; 

  up_limit CONSTANT order_tems.total_units%type := 20; 

  message VARCHAR2(50); 

BEGIN 

  FOR product_rec in product_quantity LOOP 

    quantity := product_rec.units;

     IF quantity > up_limit THEN 

        RAISE huge_quantity; 

     ELSIF quantity < up_limit THEN 

      v_message:= 'The number of unit is below the discount limit.'; 

     END IF; 

     Dbms_output.put_line (message); 

  END LOOP; 

 EXCEPTION 

   WHEN huge_quantity THEN 

 raise_application_error(-2100, 'The number of unit is above the discount limit.');

 END; 

/ 

PL/sql records

PL/SQL Records

What are records?

Records are another type of datatypes which oracle allows to be defined as a placeholder. Records are composite datatypes, which means it is a combination of different scalar datatypes like char, varchar, number etc.  Each scalar data types in the record holds a value. A record can be visualized as a row of data. It can contain all the contents of a row.
Declaring a record:
To declare a record, you must first define a composite datatype; then declare a record for that type.
The General Syntax to define a composite datatype is:

TYPE record_type_name IS RECORD

(first_col_name column_datatype,

second_col_name column_datatype, ...);

    record_type_name – it is the name of the composite type you want to define.
    first_col_name, second_col_name, etc.,- it is the names the fields/columns within the record.
    column_datatype defines the scalar datatype of the fields.


There are different ways you can declare the datatype of the fields.

1) You can declare the field in the same way as you declare the fieds while creating the table.
2) If a field is based on a column from database table, you can define the field_type as follows:

col_name table_name.column_name%type;

By declaring the field datatype in the above method, the datatype of the column is dynamically applied to the field.  This method is useful when you are altering the column specification of the table, because you do not need to change the code again.
NOTE: You can use also %type to declare variables and constants.

The General Syntax to declare a record of a uer-defined datatype is:

record_name record_type_name;

The following code shows how to declare a record called employee_rec based on a user-defined type.

DECLARE

TYPE employee_type IS RECORD

(employee_id number(5),

 employee_first_name varchar2(25),

 employee_last_name employee.last_name%type,

 employee_dept employee.dept%type);

 employee_salary employee.salary%type;

 employee_rec employee_type;

If all the fields of a record are based on the columns of a table, we can declare the record as follows:

record_name table_name%ROWTYPE;

For example, the above declaration of employee_rec can as follows:

DECLARE

 employee_rec employee%ROWTYPE;

The advantages of declaring the record as a ROWTYPE are:
1)  You do not need to explicitly declare variables for all the columns in a table.
2) If you alter the column specification in the database table, you do not need to update the code.

The disadvantage of declaring the record as a ROWTYPE is:
1) When u create a record as a ROWTYPE, fields will be created for all the columns in the table and memory will be used to create the datatype for all the fields. So use ROWTYPE only when you are using all the columns of the table in the program.

NOTE: When you are creating a record, you are just creating a datatype, similar to creating a variable. You need to assign values to the record to use them.

The following table consolidates the different ways in which you can define and declare a pl/sql record.

Syntax    

Usage

TYPE record_type_name IS RECORD (column_name1 datatype, column_name2 datatype, ...);
   

Define a composite datatype, where each field is scalar.

col_name table_name.column_name%type;
   

Dynamically define the datatype of a column based on a database column.

record_name record_type_name;
   

Declare a record based on a user-defined type.

record_name table_name%ROWTYPE;
    Dynamically declare a record based on an entire row of a table. Each column in the table corresponds to a field in the record.

Passing Values To and From a Record

When you assign values to a record, you actually assign values to the fields within it.
The General Syntax to assign a value to a column within a record direclty is:

record_name.col_name := value;

If you used %ROWTYPE to declare a record, you can assign values as shown:

record_name.column_name := value; 

We can assign values to records using SELECT Statements as shown:

SELECT col1, col2

INTO record_name.col_name1, record_name.col_name2

FROM table_name

[WHERE clause];
If %ROWTYPE is used to declare a record then you can directly assign values to the whole record instead of each columns separately. In this case, you must SELECT all the columns from the table into the record as shown:

SELECT * INTO record_name

FROM table_name

[WHERE clause];

Lets see how we can get values from a record.
The General Syntax to retrieve a value from a specific field into another variable is:

var_name := record_name.col_name;

The following table consolidates the different ways you can assign values to and from a record:
Syntax    

Usage

record_name.col_name := value;
   

To directly assign a value to a specific column of a record.

record_name.column_name := value;
   

To directly assign a value to a specific column of a record, if the record is declared using %ROWTYPE.

SELECT col1, col2 INTO record_name.col_name1, record_name.col_name2 FROM table_name [WHERE clause];
   

To assign values to each field of a record from the database table.

SELECT * INTO record_name FROM table_name [WHERE clause];
   

To assign a value to all fields in the record from a database table.

variable_name := record_name.col_name;
   

To get a value from a record column and assigning it to a variable.

PL/sql condition statements

Conditional Statements in PL/SQL

As the name implies, PL/SQL supports programming language features like conditional statements, iterative statements.

The programming constructs are similar to how you use in programming languages like Java and C++. In this section I will provide you syntax of how to use conditional statements in PL/SQL programming.

IF THEN ELSE STATEMENT

1)

IF condition 

THEN 

 statement 1; 

ELSE 

 statement 2; 

END IF;

2)

IF condition 1 

THEN 

 statement 1; 

 statement 2; 

ELSIF condtion2 THEN 

 statement 3; 

ELSE 

 statement 4; 

END IF

3)

IF condition 1 

THEN 

 statement 1; 

 statement 2; 

ELSIF condtion2 THEN 

 statement 3; 

ELSE 

 statement 4; 

END IF;

4)

IF condition1 THEN 

ELSE 

 IF condition2 THEN 

 statement1; 

 END IF; 

ELSIF condition3 THEN 

  statement2; 

END IF;

PL/sql placeholder

Advantages of PL/SQL
These are the advantages of PL/SQL.

    Block Structures: PL SQL consists of blocks of code, which can be nested within each other. Each block forms a unit of a task or a logical module. PL/SQL Blocks can be stored in the database and reused.

     Procedural Language Capability: PL SQL consists of procedural language constructs such as conditional statements (if else statements) and loops like (FOR loops).

     Better Performance: PL SQL engine processes multiple SQL statements simultaneously as a single block, thereby reducing network traffic.
    Error Handling: PL/SQL handles errors or exceptions effectively during the execution of a PL/SQL program. Once an exception is caught, specific actions can be taken depending upon the type of the exception or it can be displayed to the user with a message.

PL/SQL Placeholders

Placeholders are temporary storage area. Placeholders can be any of Variables, Constants and Records. Oracle defines placeholders to store data temporarily, which are used to manipulate data during the execution of a PL SQL block.
Depending on the kind of data you want to store, you can define placeholders with a name and a datatype. Few of the datatypes used to define placeholders are as given below.
Number (n,m) , Char (n) , Varchar2 (n) , Date , Long , Long raw, Raw, Blob, Clob, Nclob, Bfile

PL/SQL Variables

These are placeholders that store the values that can change through the PL/SQL Block.

The General Syntax to declare a variable is:

variable_name datatype [NOT NULL := value ];
    variable_name is the name of the variable.
    datatype is a valid PL/SQL datatype.
    NOT NULL is an optional specification on the variable.
    value or DEFAULT valueis also an optional specification, where you can initialize a variable.
    Each variable declaration is a separate statement and must be terminated by a semicolon.


For example, if you want to store the current salary of an employee, you can use a variable.

DECLARE

salary  number (6);

* “salary” is a variable of datatype number and of length 6.

When a variable is specified as NOT NULL, you must initialize the variable when it is declared.

For example: The below example declares two variables, one of which is a not null.

DECLARE

salary number(4);

dept varchar2(10) NOT NULL := “HR Dept”;
The value of a variable can change in the execution or exception section of the PL/SQL Block. We can assign values to variables in the two ways given below.

1) We can directly assign values to variables.
    The General Syntax is:        

  variable_name:=  value;

2) We can assign values to variables directly from the database columns by using a SELECT.. INTO statement. The General Syntax is:

SELECT column_name

INTO variable_name

FROM table_name

[WHERE condition];

Example: The below program will get the salary of an employee with id '1116' and display it on the screen.

DECLARE

 var_salary number(6);

 var_emp_id number(6) = 1116;

BEGIN

 SELECT salary

 INTO var_salary

 FROM employee

 WHERE emp_id = var_emp_id;

 dbms_output.put_line(var_salary);

 dbms_output.put_line('The employee '

      || var_emp_id || ' has  salary  ' || var_salary);

END;

/

NOTE: The backward slash '/' in the above program indicates to execute the above PL/SQL Block.

Scope of Variables

PL/SQL allows the nesting of Blocks within Blocks i.e, the Execution section of an outer block can contain inner blocks. Therefore, a variable which is accessible to an outer Block is also accessible to all nested inner Blocks. The variables declared in the inner blocks are not accessible to outer blocks. Based on their declaration we can classify variables into two types.

    Local variables - These are declared in a inner block and cannot be referenced by outside Blocks.
    Global variables - These are declared in a outer block and can be referenced by its itself and by its inner blocks.

For Example: In the below example we are creating two variables in the outer block and assigning thier product to the third variable created in the inner block. The variable 'var_mult' is declared in the inner block, so cannot be accessed in the outer block i.e. it cannot be accessed after line 11. The variables 'var_num1' and 'var_num2' can be accessed anywhere in the block.

1> DECLARE

2>  var_num1 number;

3>  var_num2 number;

4> BEGIN

5>  var_num1 := 100;

6>  var_num2 := 200;

7>  DECLARE

8>   var_mult number;

9>   BEGIN

10>    var_mult := var_num1 * var_num2;

11>   END;

12> END;

13> /

PL/SQL Introduction

What is PL/SQL?

PL/SQL stands for Procedural Language extension of SQL.

PL/SQL is a combination of SQL along with the procedural features of programming languages. It was developed by Oracle Corporation in the early 90’s to enhance the capabilities of SQL.


The PL/SQL Engine:

Oracle uses a PL/SQL engine to processes the PL/SQL statements. A PL/SQL code can be stored in the client system (client-side) or in the database (server-side).
About This PL SQL Programming tutorial

This Oracle PL SQL tutorial teaches you the basics of programming in PL/SQL with appropriate examples. You can use this tutorial as your guide or reference while programming with PL SQL. I will be making this Oracle PL SQL programming tutorial as often as possible to share my knowledge in PL SQL and help you in learning PL SQL better.

Even though the programming concepts discussed in this tutorial is specific to Oracle PL SQL. The concepts like cursors, functions and stored procedures can be used in other database systems like Sybase , Microsoft SQL server etc, with some change in syntax. This tutorial will be growing regularly; let us know if any topic related to PL SQL needs to be added or you can also share your knowledge on PL SQL with us. Lets share our knowledge about PL SQL with others.
A Simple PL/SQL Block:

Each PL/SQL program consists of SQL and PL/SQL statements which from a PL/SQL block.

A PL/SQL Block consists of three sections:

    The Declaration section (optional).
    The Execution section (mandatory).
    The Exception (or Error) Handling section (optional).

Declaration Section:
The Declaration section of a PL/SQL Block starts with the reserved keyword DECLARE. This section is optional and is used to declare any placeholders like variables, constants, records and cursors, which are used to manipulate data in the execution section. Placeholders may be any of Variables, Constants and Records, which stores data temporarily. Cursors are also declared in this section.

Execution Section:
The Execution section of a PL/SQL Block starts with the reserved keyword BEGIN and ends with END. This is a mandatory section and is the section where the program logic is written to perform any task. The programmatic constructs like loops, conditional statement and SQL statements form the part of execution section.

Exception Section:
The Exception section of a PL/SQL Block starts with the reserved keyword EXCEPTION. This section is optional. Any errors in the program can be handled in this section, so that the PL/SQL Blocks terminates gracefully. If the PL/SQL Block contains exceptions that cannot be handled, the Block terminates abruptly with errors.

Every statement in the above three sections must end with a semicolon ; . PL/SQL blocks can be nested within other PL/SQL blocks. Comments can be used to document code.

This is how a sample PL/SQL Block looks.

DECLARE
     Variable declaration
BEGIN
     Program Execution
EXCEPTION
     Exception handling
END;