In this chapter, we will discuss Exceptions in PL/SQL. An exception is an error condition during a program execution. PL/SQL supports programmers to catch such conditions using EXCEPTION block in the program and an appropriate action is taken against the error condition. There are two types of exceptions −

• System-defined exceptions
• User-defined exceptions

Syntax for Exception Handling

The general syntax for exception handling is as follows. Here you can list down as many exceptions as you can handle. The default exception will be handled using WHEN others THEN −

DECLARE
   <declarations section>
BEGIN
   <executable command(s)>
EXCEPTION
   <exception handling goes here >
   WHEN exception1 THEN
      exception1-handling-statements
   WHEN exception2  THEN
      exception2-handling-statements
   WHEN exception3 THEN
      exception3-handling-statements
   ........
   WHEN others THEN
      exception3-handling-statements
END;

Example

Let us write a code to illustrate the concept. We will be using the CUSTOMERS table we had created and used in the previous chapters −

DECLARE
   c_id customers.id%type := 8;
   c_name customerS.Name%type;
   c_addr customers.address%type;
BEGIN
   SELECT  name, address INTO  c_name, c_addr
   FROM customers
   WHERE id = c_id;
   DBMS_OUTPUT.PUT_LINE (''Name: ''||  c_name);
   DBMS_OUTPUT.PUT_LINE (''Address: '' || c_addr);

EXCEPTION
   WHEN no_data_found THEN
      dbms_output.put_line(''No such customer!'');
   WHEN others THEN
      dbms_output.put_line(''Error!'');
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

No such customer!

PL/SQL procedure successfully completed.

The above program displays the name and address of a customer whose ID is given. Since there is no customer with ID value 8 in our database, the program raises the run-time exception NO_DATA_FOUND, which is captured in the EXCEPTION block.

Raising Exceptions

Exceptions are raised by the database server automatically whenever there is any internal database error, but exceptions can be raised explicitly by the programmer by using the command RAISE. Following is the simple syntax for raising an exception −

DECLARE
   exception_name EXCEPTION;
BEGIN
   IF condition THEN
      RAISE exception_name;
   END IF;
EXCEPTION
   WHEN exception_name THEN
   statement;
END;

You can use the above syntax in raising the Oracle standard exception or any user-defined exception. In the next section, we will give you an example on raising a user-defined exception. You can raise the Oracle standard exceptions in a similar way.

User-defined Exceptions

PL/SQL allows you to define your own exceptions according to the need of your program. A user-defined exception must be declared and then raised explicitly, using either a RAISE statement or the procedure DBMS_STANDARD.RAISE_APPLICATION_ERROR.

The syntax for declaring an exception is −

DECLARE
   my-exception EXCEPTION;

Example

The following example illustrates the concept. This program asks for a customer ID, when the user enters an invalid ID, the exception invalid_id is raised.

DECLARE
   c_id customers.id%type := &cc_id;
   c_name customerS.Name%type;
   c_addr customers.address%type;
   -- user defined exception
   ex_invalid_id  EXCEPTION;
BEGIN
   IF c_id <= 0 THEN
      RAISE ex_invalid_id;
   ELSE
      SELECT  name, address INTO  c_name, c_addr
      FROM customers
      WHERE id = c_id;
      DBMS_OUTPUT.PUT_LINE (''Name: ''||  c_name);
      DBMS_OUTPUT.PUT_LINE (''Address: '' || c_addr);
   END IF;

EXCEPTION
   WHEN ex_invalid_id THEN
      dbms_output.put_line(''ID must be greater than zero!'');
   WHEN no_data_found THEN
      dbms_output.put_line(''No such customer!'');
   WHEN others THEN
      dbms_output.put_line(''Error!'');
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

Enter value for cc_id: -6 (let''s enter a value -6)
old  2: c_id customers.id%type := &cc_id;
new  2: c_id customers.id%type := -6;
ID must be greater than zero!

PL/SQL procedure successfully completed.

Pre-defined Exceptions

PL/SQL provides many pre-defined exceptions, which are executed when any database rule is violated by a program. For example, the predefined exception NO_DATA_FOUND is raised when a SELECT INTO statement returns no rows. The following table lists few of the important pre-defined exceptions −

In this chapter, we will discuss the cursors in PL/SQL. Oracle creates a memory area, known as the context area, for processing an SQL statement, which contains all the information needed for processing the statement; for example, the number of rows processed, etc.

A cursor is a pointer to this context area. PL/SQL controls the context area through a cursor. A cursor holds the rows (one or more) returned by a SQL statement. The set of rows the cursor holds is referred to as the active set.

You can name a cursor so that it could be referred to in a program to fetch and process the rows returned by the SQL statement, one at a time. There are two types of cursors −

• Implicit cursors
• Explicit cursors

Implicit Cursors

Implicit cursors are automatically created by Oracle whenever an SQL statement is executed, when there is no explicit cursor for the statement. Programmers cannot control the implicit cursors and the information in it.

Whenever a DML statement (INSERT, UPDATE and DELETE) is issued, an implicit cursor is associated with this statement. For INSERT operations, the cursor holds the data that needs to be inserted. For UPDATE and DELETE operations, the cursor identifies the rows that would be affected.

In PL/SQL, you can refer to the most recent implicit cursor as the SQL cursor, which always has attributes such as %FOUND, %ISOPEN, %NOTFOUND, and %ROWCOUNT. The SQL cursor has additional attributes, %BULK_ROWCOUNT and %BULK_EXCEPTIONS, designed for use with the FORALL statement. The following table provides the description of the most used attributes −

Any SQL cursor attribute will be accessed as sql%attribute_name as shown below in the example.

Example

We will be using the CUSTOMERS table we had created and used in the previous chapters.

Select * from customers;

+----+----------+-----+-----------+----------+
| ID | NAME     | AGE | ADDRESS   | SALARY   |
+----+----------+-----+-----------+----------+
|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
|  2 | Khilan   |  25 | Delhi     |  1500.00 |
|  3 | kaushik  |  23 | Kota      |  2000.00 |
|  4 | Chaitali |  25 | Mumbai    |  6500.00 |
|  5 | Hardik   |  27 | Bhopal    |  8500.00 |
|  6 | Komal    |  22 | MP        |  4500.00 |
+----+----------+-----+-----------+----------+

The following program will update the table and increase the salary of each customer by 500 and use the SQL%ROWCOUNT attribute to determine the number of rows affected −

DECLARE
   total_rows number(2);
BEGIN
   UPDATE customers
   SET salary = salary + 500;
   IF sql%notfound THEN
      dbms_output.put_line(''no customers selected'');
   ELSIF sql%found THEN
      total_rows := sql%rowcount;
      dbms_output.put_line( total_rows || '' customers selected '');
   END IF;
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

6 customers selected

PL/SQL procedure successfully completed.

If you check the records in customers table, you will find that the rows have been updated −

Select * from customers;

+----+----------+-----+-----------+----------+
| ID | NAME     | AGE | ADDRESS   | SALARY   |
+----+----------+-----+-----------+----------+
|  1 | Ramesh   |  32 | Ahmedabad |  2500.00 |
|  2 | Khilan   |  25 | Delhi     |  2000.00 |
|  3 | kaushik  |  23 | Kota      |  2500.00 |
|  4 | Chaitali |  25 | Mumbai    |  7000.00 |
|  5 | Hardik   |  27 | Bhopal    |  9000.00 |
|  6 | Komal    |  22 | MP        |  5000.00 |
+----+----------+-----+-----------+----------+

Explicit Cursors

Explicit cursors are programmer-defined cursors for gaining more control over the context area. An explicit cursor should be defined in the declaration section of the PL/SQL Block. It is created on a SELECT Statement which returns more than one row.

The syntax for creating an explicit cursor is −

CURSOR cursor_name IS select_statement;

Working with an explicit cursor includes the following steps −

• Declaring the cursor for initializing the memory
• Opening the cursor for allocating the memory
• Fetching the cursor for retrieving the data
• Closing the cursor to release the allocated memory

Declaring the Cursor

Declaring the cursor defines the cursor with a name and the associated SELECT statement. For example −

CURSOR c_customers IS
   SELECT id, name, address FROM customers;

Opening the Cursor

Opening the cursor allocates the memory for the cursor and makes it ready for fetching the rows returned by the SQL statement into it. For example, we will open the above defined cursor as follows −

OPEN c_customers;

Fetching the Cursor

Fetching the cursor involves accessing one row at a time. For example, we will fetch rows from the above-opened cursor as follows −

FETCH c_customers INTO c_id, c_name, c_addr;

Closing the Cursor

Closing the cursor means releasing the allocated memory. For example, we will close the above-opened cursor as follows −

CLOSE c_customers;

Example

Following is a complete example to illustrate the concepts of explicit cursors &minua;

DECLARE
   c_id customers.id%type;
   c_name customers.name%type;
   c_addr customers.address%type;
   CURSOR c_customers is
      SELECT id, name, address FROM customers;
BEGIN
   OPEN c_customers;
   LOOP
   FETCH c_customers into c_id, c_name, c_addr;
      EXIT WHEN c_customers%notfound;
      dbms_output.put_line(c_id || '' '' || c_name || '' '' || c_addr);
   END LOOP;
   CLOSE c_customers;
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

1 Ramesh Ahmedabad
2 Khilan Delhi
3 kaushik Kota
4 Chaitali Mumbai
5 Hardik Bhopal
6 Komal MP

PL/SQL procedure successfully completed.

In this chapter, we will discuss arrays in PL/SQL. The PL/SQL programming language provides a data structure called the VARRAY, which can store a fixed-size sequential collection of elements of the same type. A varray is used to store an ordered collection of data, however it is often better to think of an array as a collection of variables of the same type.

All varrays consist of contiguous memory locations. The lowest address corresponds to the first element and the highest address to the last element.

An array is a part of collection type data and it stands for variable-size arrays. We will study other collection types in a later chapter ”PL/SQL Collections”.

Each element in a varray has an index associated with it. It also has a maximum size that can be changed dynamically.

Creating a Varray Type

A varray type is created with the CREATE TYPE statement. You must specify the maximum size and the type of elements stored in the varray.

The basic syntax for creating a VARRAY type at the schema level is −

CREATE OR REPLACE TYPE varray_type_name IS VARRAY(n) of <element_type>

Where,

• varray_type_name is a valid attribute name,
• n is the number of elements (maximum) in the varray,
• element_type is the data type of the elements of the array.

Maximum size of a varray can be changed using the ALTER TYPE statement.

For example,

CREATE Or REPLACE TYPE namearray AS VARRAY(3) OF VARCHAR2(10);
/

Type created.

The basic syntax for creating a VARRAY type within a PL/SQL block is −

TYPE varray_type_name IS VARRAY(n) of <element_type>

For example −

TYPE namearray IS VARRAY(5) OF VARCHAR2(10);
Type grades IS VARRAY(5) OF INTEGER;

Let us now work out on a few examples to understand the concept −

Example 1

The following program illustrates the use of varrays −

DECLARE
   type namesarray IS VARRAY(5) OF VARCHAR2(10);
   type grades IS VARRAY(5) OF INTEGER;
   names namesarray;
   marks grades;
   total integer;
BEGIN
   names := namesarray(''Kavita'', ''Pritam'', ''Ayan'', ''Rishav'', ''Aziz'');
   marks:= grades(98, 97, 78, 87, 92);
   total := names.count;
   dbms_output.put_line(''Total ''|| total || '' Students'');
   FOR i in 1 .. total LOOP
      dbms_output.put_line(''Student: '' || names(i) || ''
      Marks: '' || marks(i));
   END LOOP;
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

Total 5 Students
Student: Kavita  Marks: 98
Student: Pritam  Marks: 97
Student: Ayan  Marks: 78
Student: Rishav  Marks: 87
Student: Aziz  Marks: 92

PL/SQL procedure successfully completed.

Please note −

• In Oracle environment, the starting index for varrays is always 1.

• You can initialize the varray elements using the constructor method of the varray type, which has the same name as the varray.

• Varrays are one-dimensional arrays.

• A varray is automatically NULL when it is declared and must be initialized before its elements can be referenced.

Example 2

Elements of a varray could also be a %ROWTYPE of any database table or %TYPE of any database table field. The following example illustrates the concept.

We will use the CUSTOMERS table stored in our database as −

Select * from customers;

+----+----------+-----+-----------+----------+
| ID | NAME     | AGE | ADDRESS   | SALARY   |
+----+----------+-----+-----------+----------+
|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
|  2 | Khilan   |  25 | Delhi     |  1500.00 |
|  3 | kaushik  |  23 | Kota      |  2000.00 |
|  4 | Chaitali |  25 | Mumbai    |  6500.00 |
|  5 | Hardik   |  27 | Bhopal    |  8500.00 |
|  6 | Komal    |  22 | MP        |  4500.00 |
+----+----------+-----+-----------+----------+

Following example makes the use of cursor, which you will study in detail in a separate chapter.

DECLARE
   CURSOR c_customers is
   SELECT  name FROM customers;
   type c_list is varray (6) of customers.name%type;
   name_list c_list := c_list();
   counter integer :=0;
BEGIN
   FOR n IN c_customers LOOP
      counter := counter + 1;
      name_list.extend;
      name_list(counter)  := n.name;
      dbms_output.put_line(''Customer(''||counter ||''):''||name_list(counter));
   END LOOP;
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

Customer(1): Ramesh
Customer(2): Khilan
Customer(3): kaushik
Customer(4): Chaitali
Customer(5): Hardik
Customer(6): Komal

PL/SQL procedure successfully completed.

In this chapter, we will discuss the functions in PL/SQL. A function is same as a procedure except that it returns a value. Therefore, all the discussions of the previous chapter are true for functions too.

Creating a Function

A standalone function is created using the CREATE FUNCTION statement. The simplified syntax for the CREATE OR REPLACE PROCEDURE statement is as follows −

CREATE [OR REPLACE] FUNCTION function_name
[(parameter_name [IN | OUT | IN OUT] type [, ...])]
RETURN return_datatype
{IS | AS}
BEGIN
   < function_body >
END [function_name];

Where,

• function-name specifies the name of the function.

• [OR REPLACE] option allows the modification of an existing function.

• The optional parameter list contains name, mode and types of the parameters. IN represents the value that will be passed from outside and OUT represents the parameter that will be used to return a value outside of the procedure.

• The function must contain a return statement.

• The RETURN clause specifies the data type you are going to return from the function.

• function-body contains the executable part.

• The AS keyword is used instead of the IS keyword for creating a standalone function.

Example

The following example illustrates how to create and call a standalone function. This function returns the total number of CUSTOMERS in the customers table.

We will use the CUSTOMERS table, which we had created in the chapter −

Select * from customers;

+----+----------+-----+-----------+----------+
| ID | NAME     | AGE | ADDRESS   | SALARY   |
+----+----------+-----+-----------+----------+
|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
|  2 | Khilan   |  25 | Delhi     |  1500.00 |
|  3 | kaushik  |  23 | Kota      |  2000.00 |
|  4 | Chaitali |  25 | Mumbai    |  6500.00 |
|  5 | Hardik   |  27 | Bhopal    |  8500.00 |
|  6 | Komal    |  22 | MP        |  4500.00 |
+----+----------+-----+-----------+----------+

CREATE OR REPLACE FUNCTION totalCustomers
RETURN number IS
   total number(2) := 0;
BEGIN
   SELECT count(*) into total
   FROM customers;

   RETURN total;
END;
/

When the above code is executed using the SQL prompt, it will produce the following result −

Function created.

Calling a Function

While creating a function, you give a definition of what the function has to do. To use a function, you will have to call that function to perform the defined task. When a program calls a function, the program control is transferred to the called function.

A called function performs the defined task and when its return statement is executed or when the last end statement is reached, it returns the program control back to the main program.

To call a function, you simply need to pass the required parameters along with the function name and if the function returns a value, then you can store the returned value. Following program calls the function totalCustomers from an anonymous block −

DECLARE
   c number(2);
BEGIN
   c := totalCustomers();
   dbms_output.put_line(''Total no. of Customers: '' || c);
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

Total no. of Customers: 6

PL/SQL procedure successfully completed.

Example

The following example demonstrates Declaring, Defining, and Invoking a Simple PL/SQL Function that computes and returns the maximum of two values.

DECLARE
   a number;
   b number;
   c number;
FUNCTION findMax(x IN number, y IN number)
RETURN number
IS
    z number;
BEGIN
   IF x > y THEN
      z:= x;
   ELSE
      Z:= y;
   END IF;
   RETURN z;
END;
BEGIN
   a:= 23;
   b:= 45;
   c := findMax(a, b);
   dbms_output.put_line('' Maximum of (23,45): '' || c);
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

Maximum of (23,45): 45

PL/SQL procedure successfully completed.

PL/SQL Recursive Functions

We have seen that a program or subprogram may call another subprogram. When a subprogram calls itself, it is referred to as a recursive call and the process is known as recursion.

To illustrate the concept, let us calculate the factorial of a number. Factorial of a number n is defined as −

n! = n*(n-1)!
   = n*(n-1)*(n-2)!
      ...
   = n*(n-1)*(n-2)*(n-3)... 1

The following program calculates the factorial of a given number by calling itself recursively −

DECLARE
   num number;
   factorial number;

FUNCTION fact(x number)
RETURN number
IS
   f number;
BEGIN
   IF x=0 THEN
      f := 1;
   ELSE
      f := x * fact(x-1);
   END IF;
RETURN f;
END;

BEGIN
   num:= 6;
   factorial := fact(num);
   dbms_output.put_line('' Factorial ''|| num || '' is '' || factorial);
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

Factorial 6 is 720

PL/SQL procedure successfully completed.

In this chapter, we will discuss Procedures in PL/SQL. A subprogram is a program unit/module that performs a particular task. These subprograms are combined to form larger programs. This is basically called the ”Modular design”. A subprogram can be invoked by another subprogram or program which is called the calling program.

A subprogram can be created −

• At the schema level
• Inside a package
• Inside a PL/SQL block

At the schema level, subprogram is a standalone subprogram. It is created with the CREATE PROCEDURE or the CREATE FUNCTION statement. It is stored in the database and can be deleted with the DROP PROCEDURE or DROP FUNCTION statement.

A subprogram created inside a package is a packaged subprogram. It is stored in the database and can be deleted only when the package is deleted with the DROP PACKAGE statement. We will discuss packages in the chapter ”PL/SQL – Packages”.

PL/SQL subprograms are named PL/SQL blocks that can be invoked with a set of parameters. PL/SQL provides two kinds of subprograms −

• Functions − These subprograms return a single value; mainly used to compute and return a value.

• Procedures − These subprograms do not return a value directly; mainly used to perform an action.

This chapter is going to cover important aspects of a PL/SQL procedure. We will discuss PL/SQL function in the next chapter.

Parts of a PL/SQL Subprogram

Each PL/SQL subprogram has a name, and may also have a parameter list. Like anonymous PL/SQL blocks, the named blocks will also have the following three parts −

Creating a Procedure

A procedure is created with the CREATE OR REPLACE PROCEDURE statement. The simplified syntax for the CREATE OR REPLACE PROCEDURE statement is as follows −

CREATE [OR REPLACE] PROCEDURE procedure_name
[(parameter_name [IN | OUT | IN OUT] type [, ...])]
{IS | AS}
BEGIN
  < procedure_body >
END procedure_name;

Where,

• procedure-name specifies the name of the procedure.

• [OR REPLACE] option allows the modification of an existing procedure.

• The optional parameter list contains name, mode and types of the parameters. IN represents the value that will be passed from outside and OUT represents the parameter that will be used to return a value outside of the procedure.

• procedure-body contains the executable part.

• The AS keyword is used instead of the IS keyword for creating a standalone procedure.

Example

The following example creates a simple procedure that displays the string ”Hello World!” on the screen when executed.

CREATE OR REPLACE PROCEDURE greetings
AS
BEGIN
   dbms_output.put_line(''Hello World!'');
END;
/

When the above code is executed using the SQL prompt, it will produce the following result −

Procedure created.

Executing a Standalone Procedure

A standalone procedure can be called in two ways −

• Using the EXECUTE keyword

• Calling the name of the procedure from a PL/SQL block

The above procedure named ”greetings” can be called with the EXECUTE keyword as −

EXECUTE greetings;

The above call will display −

Hello World

PL/SQL procedure successfully completed.

The procedure can also be called from another PL/SQL block −

BEGIN
   greetings;
END;
/

The above call will display −

Hello World

PL/SQL procedure successfully completed.

Deleting a Standalone Procedure

A standalone procedure is deleted with the DROP PROCEDURE statement. Syntax for deleting a procedure is −

DROP PROCEDURE procedure-name;

You can drop the greetings procedure by using the following statement −

DROP PROCEDURE greetings;

Parameter Modes in PL/SQL Subprograms

The following table lists out the parameter modes in PL/SQL subprograms −

IN & OUT Mode Example 1

This program finds the minimum of two values. Here, the procedure takes two numbers using the IN mode and returns their minimum using the OUT parameters.

DECLARE
   a number;
   b number;
   c number;
PROCEDURE findMin(x IN number, y IN number, z OUT number) IS
BEGIN
   IF x < y THEN
      z:= x;
   ELSE
      z:= y;
   END IF;
END;
BEGIN
   a:= 23;
   b:= 45;
   findMin(a, b, c);
   dbms_output.put_line('' Minimum of (23, 45) : '' || c);
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

Minimum of (23, 45) : 23

PL/SQL procedure successfully completed.

IN & OUT Mode Example 2

This procedure computes the square of value of a passed value. This example shows how we can use the same parameter to accept a value and then return another result.

DECLARE
   a number;
PROCEDURE squareNum(x IN OUT number) IS
BEGIN
  x := x * x;
END;
BEGIN
   a:= 23;
   squareNum(a);
   dbms_output.put_line('' Square of (23): '' || a);
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

Square of (23): 529

PL/SQL procedure successfully completed.

Methods for Passing Parameters

Actual parameters can be passed in three ways −

• Positional notation
• Named notation
• Mixed notation

Positional Notation

In positional notation, you can call the procedure as −

findMin(a, b, c, d);

In positional notation, the first actual parameter is substituted for the first formal parameter; the second actual parameter is substituted for the second formal parameter, and so on. So, a is substituted for x, b is substituted for y, c is substituted for z and d is substituted for m.

Named Notation

In named notation, the actual parameter is associated with the formal parameter using the arrow symbol ( => ). The procedure call will be like the following −

findMin(x => a, y => b, z => c, m => d);

Mixed Notation

In mixed notation, you can mix both notations in procedure call; however, the positional notation should precede the named notation.

The following call is legal −

findMin(a, b, c, m => d);

However, this is not legal:

findMin(x => a, b, c, d);

The string in PL/SQL is actually a sequence of characters with an optional size specification. The characters could be numeric, letters, blank, special characters or a combination of all. PL/SQL offers three kinds of strings −

• Fixed-length strings − In such strings, programmers specify the length while declaring the string. The string is right-padded with spaces to the length so specified.

• Variable-length strings − In such strings, a maximum length up to 32,767, for the string is specified and no padding takes place.

• Character large objects (CLOBs) − These are variable-length strings that can be up to 128 terabytes.

PL/SQL strings could be either variables or literals. A string literal is enclosed within quotation marks. For example,

''This is a string literal.'' Or ''hello world''

To include a single quote inside a string literal, you need to type two single quotes next to one another. For example,

''this isn''''t what it looks like''

Declaring String Variables

Oracle database provides numerous string datatypes, such as CHAR, NCHAR, VARCHAR2, NVARCHAR2, CLOB, and NCLOB. The datatypes prefixed with an ”N” are ”national character set” datatypes, that store Unicode character data.

If you need to declare a variable-length string, you must provide the maximum length of that string. For example, the VARCHAR2 data type. The following example illustrates declaring and using some string variables −

DECLARE
   name varchar2(20);
   company varchar2(30);
   introduction clob;
   choice char(1);
BEGIN
   name := ''John Smith
   company := ''Infotech
   introduction := '' Hello! I''''m John Smith from Infotech.
   choice := ''y
   IF choice = ''y'' THEN
      dbms_output.put_line(name);
      dbms_output.put_line(company);
      dbms_output.put_line(introduction);
   END IF;
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

John Smith
Infotech
Hello! I''m John Smith from Infotech.

PL/SQL procedure successfully completed

To declare a fixed-length string, use the CHAR datatype. Here you do not have to specify a maximum length for a fixed-length variable. If you leave off the length constraint, Oracle Database automatically uses a maximum length required. The following two declarations are identical −

red_flag CHAR(1) := ''Y
 red_flag CHAR   := ''Y

PL/SQL String Functions and Operators

PL/SQL offers the concatenation operator (||) for joining two strings. The following table provides the string functions provided by PL/SQL −

Let us now work out on a few examples to understand the concept −

Example 1

DECLARE
   greetings varchar2(11) := ''hello world
BEGIN
   dbms_output.put_line(UPPER(greetings));

   dbms_output.put_line(LOWER(greetings));

   dbms_output.put_line(INITCAP(greetings));

   /* retrieve the first character in the string */
   dbms_output.put_line ( SUBSTR (greetings, 1, 1));

   /* retrieve the last character in the string */
   dbms_output.put_line ( SUBSTR (greetings, -1, 1));

   /* retrieve five characters,
      starting from the seventh position. */
   dbms_output.put_line ( SUBSTR (greetings, 7, 5));

   /* retrieve the remainder of the string,
      starting from the second position. */
   dbms_output.put_line ( SUBSTR (greetings, 2));

   /* find the location of the first "e" */
   dbms_output.put_line ( INSTR (greetings, ''e''));
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

HELLO WORLD
hello world
Hello World
h
d
World
ello World
2

PL/SQL procedure successfully completed.

Example 2

DECLARE
   greetings varchar2(30) := ''......Hello World.....
BEGIN
   dbms_output.put_line(RTRIM(greetings,''.''));
   dbms_output.put_line(LTRIM(greetings, ''.''));
   dbms_output.put_line(TRIM( ''.'' from greetings));
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

......Hello World
Hello World.....
Hello World

PL/SQL procedure successfully completed.

In this chapter, we will discuss operators in PL/SQL. An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulation. PL/SQL language is rich in built-in operators and provides the following types of operators −

• Arithmetic operators
• Relational operators
• Comparison operators
• Logical operators
• String operators

Here, we will understand the arithmetic, relational, comparison and logical operators one by one. The String operators will be discussed in a later chapter − PL/SQL – Strings.

Arithmetic Operators

Following table shows all the arithmetic operators supported by PL/SQL. Let us assume variable A holds 10 and variable B holds 5, then −

Relational Operators

Relational operators compare two expressions or values and return a Boolean result. Following table shows all the relational operators supported by PL/SQL. Let us assume variable A holds 10 and variable B holds 20, then −

Comparison Operators

Comparison operators are used for comparing one expression to another. The result is always either TRUE, FALSE or NULL.

Logical Operators

Following table shows the Logical operators supported by PL/SQL. All these operators work on Boolean operands and produce Boolean results. Let us assume variable A holds true and variable B holds false, then −

PL/SQL Operator Precedence

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator.

For example, x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator * has higher precedence than +, so it first gets multiplied with 3*2 and then adds into 7.

Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.

The precedence of operators goes as follows: =, <, >, <=, >=, <>, !=, ~=, ^=, IS NULL, LIKE, BETWEEN, IN.

In this chapter, we will discuss constants and literals in PL/SQL. A constant holds a value that once declared, does not change in the program. A constant declaration specifies its name, data type, and value, and allocates storage for it. The declaration can also impose the NOT NULL constraint.

Declaring a Constant

A constant is declared using the CONSTANT keyword. It requires an initial value and does not allow that value to be changed. For example −

PI CONSTANT NUMBER := 3.141592654;
DECLARE
   -- constant declaration
   pi constant number := 3.141592654;
   -- other declarations
   radius number(5,2);
   dia number(5,2);
   circumference number(7, 2);
   area number (10, 2);
BEGIN
   -- processing
   radius := 9.5;
   dia := radius * 2;
   circumference := 2.0 * pi * radius;
   area := pi * radius * radius;
   -- output
   dbms_output.put_line(''Radius: '' || radius);
   dbms_output.put_line(''Diameter: '' || dia);
   dbms_output.put_line(''Circumference: '' || circumference);
   dbms_output.put_line(''Area: '' || area);
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

Radius: 9.5
Diameter: 19
Circumference: 59.69
Area: 283.53

Pl/SQL procedure successfully completed.

The PL/SQL Literals

A literal is an explicit numeric, character, string, or Boolean value not represented by an identifier. For example, TRUE, 786, NULL, ”tutorialspoint” are all literals of type Boolean, number, or string. PL/SQL, literals are case-sensitive. PL/SQL supports the following kinds of literals −

• Numeric Literals
• Character Literals
• String Literals
• BOOLEAN Literals
• Date and Time Literals

The following table provides examples from all these categories of literal values.

To embed single quotes within a string literal, place two single quotes next to each other as shown in the following program −

DECLARE
   message  varchar2(30):= ''That''''s tutorialspoint.com!
BEGIN
   dbms_output.put_line(message);
END;
/

When the above code is executed at the SQL prompt, it produces the following result −

That''s tutorialspoint.com!

PL/SQL procedure successfully completed.

In this chapter, we will discuss the Environment Setup of PL/SQL. PL/SQL is not a standalone programming language; it is a tool within the Oracle programming environment. SQL* Plus is an interactive tool that allows you to type SQL and PL/SQL statements at the command prompt. These commands are then sent to the database for processing. Once the statements are processed, the results are sent back and displayed on screen.

To run PL/SQL programs, you should have the Oracle RDBMS Server installed in your machine. This will take care of the execution of the SQL commands. The most recent version of Oracle RDBMS is 11g. You can download a trial version of Oracle 11g from the following link −

You will have to download either the 32-bit or the 64-bit version of the installation as per your operating system. Usually there are two files. We have downloaded the 64-bit version. You will also use similar steps on your operating system, does not matter if it is Linux or Solaris.

• win64_11gR2_database_1of2.zip

• win64_11gR2_database_2of2.zip

After downloading the above two files, you will need to unzip them in a single directory database and under that you will find the following sub-directories −

Step 1

Let us now launch the Oracle Database Installer using the setup file. Following is the first screen. You can provide your email ID and check the checkbox as shown in the following screenshot. Click the Next button.

Step 2

You will be directed to the following screen; uncheck the checkbox and click the Continue button to proceed.

Step 3

Just select the first option Create and Configure Database using the radio button and click the Next button to proceed.

Step 4

We assume you are installing Oracle for the basic purpose of learning and that you are installing it on your PC or Laptop. Thus, select the Desktop Class option and click the Next button to proceed.

Step 5

Provide a location, where you will install the Oracle Server. Just modify the Oracle Base and the other locations will set automatically. You will also have to provide a password; this will be used by the system DBA. Once you provide the required information, click the Next button to proceed.

Step 6

Again, click the Next button to proceed.

Step 7

Click the Finish button to proceed; this will start the actual server installation.

Step 8

This will take a few moments, until Oracle starts performing the required configuration.

Step 9

Here, Oracle installation will copy the required configuration files. This should take a moment −

Step 10

Once the database files are copied, you will have the following dialogue box. Just click the OK button and come out.

Step 11

Upon installation, you will have the following final window.

Final Step

It is now time to verify your installation. At the command prompt, use the following command if you are using Windows −

sqlplus "/ as sysdba"

You should have the SQL prompt where you will write your PL/SQL commands and scripts −

Text Editor

Running large programs from the command prompt may land you in inadvertently losing some of the work. It is always recommended to use the command files. To use the command files −

• Type your code in a text editor, like Notepad, Notepad+, or EditPlus, etc.

• Save the file with the .sql extension in the home directory.

• Launch the SQL*Plus command prompt from the directory where you created your PL/SQL file.

• Type @file_name at the SQL*Plus command prompt to execute your program.

If you are not using a file to execute the PL/SQL scripts, then simply copy your PL/SQL code and right-click on the black window that displays the SQL prompt; use the paste option to paste the complete code at the command prompt. Finally, just press Enter to execute the code, if it is not already executed.

In this chapter, we will discuss conditions in PL/SQL. Decision-making structures require that the programmer specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

Following is the general form of a typical conditional (i.e., decision making) structure found in most of the programming languages −

PL/SQL programming language provides following types of decision-making statements. Click the following links to check their detail.