Master the Power of Cursor Parameters in PL/SQL

Table of Contents

1. Introduction
2. What is a Parameterized Cursor?
3. Syntax of Parameterized Cursor
4. Opening a Parameterized Cursor
5. Example Program: Working with Parameterized Cursor
6. Parameterized Cursor with Default Values
7. Example Program: Parameterized Cursor with Default Values
8. Conclusion
9. FAQ

Introduction

In this article, we will discuss parameterized cursors, which are cursors with arguments or parameters. Parameterized cursors allow us to Create dynamic SQL queries with conditions containing variables. We will explore the syntax of parameterized cursors, how to open them, and provide examples to illustrate their usage. Additionally, we will cover parameterized cursors with default values to handle situations where values are not explicitly provided.

What is a Parameterized Cursor?

A parameterized cursor is a Type of cursor that accepts arguments or parameters. Unlike regular cursors, parameterized cursors allow us to create dynamic SQL queries with conditions that contain variables. By passing parameters to the cursor, we can filter the query results Based on the provided values. This feature enables us to create more flexible and customizable queries.

Syntax of Parameterized Cursor

To declare a parameterized cursor, use the following syntax:

  select_statement;```

Here, cursor_name is the name of the cursor you want to create, variable_name is the name of the parameter variable, and data_type is the data type of the parameter variable. The select_statement represents the SQL query you want to associate with the cursor.

# Opening a Parameterized Cursor

After declaring a parameterized cursor, you need to open it by providing values for the parameters. To open a cursor, use the open keyword followed by the cursor name and the value or variable you want to assign to the parameter. The syntax for opening a cursor is as follows:

```open cursor_name(value/variable/expression);```

Here, cursor_name is the name of the cursor you want to open, and value/variable/expression represents the value, variable, or expression you want to assign to the parameter.

# Example Program: Working with Parameterized Cursor

Let's consider a simple program to demonstrate the usage of a parameterized cursor. We will use SQL Plus for this example. Here is the program:

```declare
  employee emp%rowtype;
  cursor c123(low number, high number) is
   select * from emp where sal between low and high;
begin
  open c123(500, 2000);

  loop
    fetch c123 into employee;
    exit when c123%notfound;

    dbms_output.put_line('Employee Number: ' || employee.empno || ' Employee Name: ' || employee.ename || ' Salary: ' || employee.sal);
  end loop;

  close c123;

  open c123(800, 2000);

  loop
    fetch c123 into employee;
    exit when c123%notfound;

    dbms_output.put_line('Employee Number: ' || employee.empno || ' Employee Name: ' || employee.ename || ' Salary: ' || employee.sal);
  end loop;

  close c123;
end;```

In this program, we declare a cursor named c123 that takes two parameters: low and high. We use these parameters to filter the query results and select employees with salaries between the low and high values. The program opens the cursor twice, each time with different parameter values, and fetches and displays the employee information within a loop. Finally, the program closes the cursor.

# Parameterized Cursor with Default Values

In some cases, we may want to provide default values for the parameters in a parameterized cursor. Default values will be used if no explicit values are provided when opening the cursor. This can be useful when working with variables that have common default values that can save us from providing the same values repeatedly.

# Example Program: Parameterized Cursor with Default Values

Let's modify the previous program to include default values for one of the parameters. Here is the updated program:

```declare
  employee emp%rowtype;
  cursor c123(low number, high number := 1000) is
   select * from emp where sal between low and high;
begin
  open c123(500);

  loop
    fetch c123 into employee;
    exit when c123%notfound;

    dbms_output.put_line('Employee Number: ' || employee.empno || ' Employee Name: ' || employee.ename || ' Salary: ' || employee.sal);
  end loop;

  close c123;

  open c123(800, 2000);

  loop
    fetch c123 into employee;
    exit when c123%notfound;

    dbms_output.put_line('Employee Number: ' || employee.empno || ' Employee Name: ' || employee.ename || ' Salary: ' || employee.sal);
  end loop;

  close c123;
end;```

In this program, we have modified the declaration of the cursor c123 by providing a default value of 1000 for the high parameter. This means that if no value is explicitly provided for the high parameter when opening the cursor, the default value of 1000 will be used. The rest of the program remains the same.

# Conclusion

Parameterized cursors are powerful tools that allow us to create dynamic SQL queries with conditions containing variables. By using parameterized cursors, we can build more flexible and customizable queries. In this article, we covered the syntax of parameterized cursors, how to open them, and provided examples of working with them. We also discussed parameterized cursors with default values, which provide a convenient way to handle situations where values are not explicitly provided.

# FAQ

**Q: What is the purpose of a parameterized cursor?**
A: The purpose of a parameterized cursor is to allow for dynamic SQL queries with conditions that contain variables. By passing parameters to a cursor, you can filter query results based on the provided values.

**Q: How do you declare a parameterized cursor?**
A: To declare a parameterized cursor, use the following syntax: `cursor cursor_name(variable_name data_type) is select_statement;` where `cursor_name` is the name of the cursor, `variable_name` is the name of the parameter variable, `data_type` is the data type of the parameter variable, and `select_statement` is the SQL query associated with the cursor.

**Q: How do you open a parameterized cursor?**
A: To open a parameterized cursor, use the `open` keyword followed by the cursor name and the value or variable to assign to the parameter. For example, `open cursor_name(value/variable/expression);` where `cursor_name` is the name of the cursor and `value/variable/expression` represents the value, variable, or expression to assign to the parameter.

**Q: Can a parameterized cursor have default values?**
A: Yes, a parameterized cursor can have default values. Default values are used when no explicit values are provided when opening the cursor. This can be useful for variables with common default values, saving you from having to provide the same values repeatedly.

**Q: How can I handle situations where values are not explicitly provided for parameters in a parameterized cursor?**
A: To handle situations where values are not explicitly provided for parameters in a parameterized cursor, you can assign default values to parameters. These default values will be used if no explicit values are provided, ensuring that the cursor still functions properly.