PL/SQL Procedure

CREATE [OR REPLACE] PROCEDURE procedure_name
    [ (parameter [,parameter]) ]

IS
    [declaration_section]

BEGIN
    executable_section

[EXCEPTION
    exception_section]

END [procedure_name];

CREATE OR REPLACE Procedure UpdateCourse
   ( name_in IN varchar2 )

IS
   cnumber number;

   cursor c1 is
   SELECT course_number
    FROM courses_tbl
    WHERE course_name = name_in;

BEGIN

   open c1;
   fetch c1 into cnumber;

   if c1%notfound then
      cnumber := 9999;
   end if;

   INSERT INTO student_courses
   ( course_name,
     course_number )
   VALUES
   ( name_in,
     cnumber );

   commit;

   close c1;

EXCEPTION
WHEN OTHERS THEN
   raise_application_error(-20001,'An error was encountered - '||SQLCODE||' -ERROR- '||SQLERRM);
END;

DROP PROCEDURE procedure_name;

DROP PROCEDURE UpdateCourse;

The PL/SQL stored procedure or simply a procedure is a PL/SQL block which performs one or more specific tasks. It is just like procedures in other programming languages.

The procedure contains a header and a body.

• Header: The header contains the name of the procedure and the parameters or variables passed to the procedure.
• Body: The body contains a declaration section, execution section and exception section similar to a general PL/SQL block.

How to pass parameters in procedure:

When you want to create a procedure or function, you have to define parameters .There is three ways to pass parameters in procedure:

1. IN parameters: The IN parameter can be referenced by the procedure or function. The value of the parameter cannot be overwritten by the procedure or the function.
2. OUT parameters: The OUT parameter cannot be referenced by the procedure or function, but the value of the parameter can be overwritten by the procedure or function.
3. INOUT parameters: The INOUT parameter can be referenced by the procedure or function and the value of the parameter can be overwritten by the procedure or function.

A procedure may or may not return any value.

PL/SQL Create Procedure

Syntax for creating procedure:

Create procedure example

In this example, we are going to insert record in user table. So you need to create user table first.

Table creation:

Now write the procedure code to insert record in user table.

Procedure Code:

Output:

Procedure created.

PL/SQL program to call procedure

Let's see the code to call above created procedure.

Now, see the "USER" table, you will see one record is inserted.

PL/SQL Drop Procedure

Syntax for drop procedure

Example of drop procedure

PL/SQL Function

The PL/SQL Function is very similar to PL/SQL Procedure. The main difference between procedure and a function is, a function must always return a value, and on the other hand a procedure may or may not return a value. Except this, all the other things of PL/SQL procedure are true for PL/SQL function too.

Syntax to create a function:

Here:

• Function_name: specifies the name of the function.
• [OR REPLACE] option allows modifying an existing function.
• The optional parameter list contains name, mode and types of the parameters.
• IN represents that value will be passed from outside and OUT represents that this parameter will be used to return a value outside of the procedure.

The function must contain a return statement.

• RETURN clause specifies that 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.

PL/SQL Function Example

Let's see a simple example to create a function.

Now write another program to call the function.

Output:

Addition is: 33
Statement processed.
0.05 seconds

Another PL/SQL Function Example

Let's take an example to demonstrate Declaring, Defining and Invoking a simple PL/SQL function which will compute and return the maximum of two values.

Output:

Maximum of (23,45): 45
Statement processed.
0.02 seconds

PL/SQL function example using table

Let's take a customer table. This example illustrates creating and calling a standalone function. This function will return the total number of CUSTOMERS in the customers table.

Create customers table and have records in it.

Create Function:

After the execution of above code, you will get the following result.

Function created.

Calling PL/SQL Function:

While creating a function, you have to 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. Once the function is called, the program control is transferred to the called function.

After the successful completion of the defined task, the call function returns program control back to the main program.

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

After the execution of above code in SQL prompt, you will get the following result.

Total no. of Customers: 4
PL/SQL procedure successfully completed.

PL/SQL Recursive Function

You already know that a program or a subprogram can call another subprogram. When a subprogram calls itself, it is called recursive call and the process is known as recursion.

Example to calculate the factorial of a number

Let's take an example to calculate the factorial of a number. This example calculates the factorial of a given number by calling itself recursively.

After the execution of above code at SQL prompt, it produces the following result.

Factorial 6 is 720
PL/SQL procedure successfully completed.

PL/SQL Drop Function

Syntax for removing your created function:

If you want to remove your created function from the database, you should use the following syntax.