Explicit Cursor vs. Implicit Cursor

Attribute	Explicit Cursor	Implicit Cursor
Declaration	Explicitly declared using the CURSOR keyword	Automatically created by Oracle for each SQL statement
Usage	Explicitly opened, fetched, and closed by the programmer	Automatically opened, fetched, and closed by Oracle
Control	Programmer has full control over the cursor	Oracle handles the cursor operations internally
Scope	Can be used within a specific PL/SQL block	Can be used within any PL/SQL block
Explicit Opening	Explicitly opened using the OPEN keyword	Automatically opened when the SQL statement is executed
Explicit Fetching	Explicitly fetched using the FETCH keyword	Automatically fetched when the cursor is opened
Explicit Closing	Explicitly closed using the CLOSE keyword	Automatically closed after the last row is fetched
Cursor Attributes	Can be accessed using the cursor name and dot notation	Cannot be accessed directly

Introduction

In Oracle, cursors are used to retrieve and manipulate data from the database. They provide a way to process result sets returned by SQL queries. Cursors can be classified into two types: explicit cursors and implicit cursors. While both types serve the same purpose, they differ in their declaration, usage, and behavior. In this article, we will explore the attributes of explicit and implicit cursors, highlighting their similarities and differences.

Implicit Cursors

Implicit cursors are automatically created by Oracle whenever a SQL statement is executed. They are used to handle single-row queries or queries that return a single row at a time. Implicit cursors are convenient to use as they do not require explicit declaration or management.

When a SQL statement is executed, Oracle automatically opens an implicit cursor, fetches the result row, and then closes the cursor. This process is transparent to the developer, making it easier to work with simple queries. However, it is important to note that implicit cursors have limitations in terms of flexibility and control.

One of the key attributes of implicit cursors is that they are read-only. This means that you cannot use them to perform DML (Data Manipulation Language) operations such as INSERT, UPDATE, or DELETE. Implicit cursors are primarily used for retrieving data from the database.

Another attribute of implicit cursors is that they do not require explicit cursor operations like opening, fetching, or closing. Oracle handles these operations automatically behind the scenes. This makes implicit cursors suitable for simple queries where you only need to retrieve a single row or perform a single operation.

Implicit cursors are also useful when you need to retrieve the value of a single column from a query result. You can directly assign the result to a variable without the need for explicit cursor operations. This simplicity and convenience make implicit cursors a popular choice for basic database operations.

Explicit Cursors

Unlike implicit cursors, explicit cursors require explicit declaration and management by the developer. They provide more control and flexibility over the result set processing. Explicit cursors are typically used for complex queries that involve multiple rows or require DML operations.

To use an explicit cursor, you need to declare it explicitly using the CURSOR keyword. The declaration includes the SELECT statement that defines the result set to be processed. Once declared, you can open the cursor, fetch rows from the result set, and close the cursor as needed.

One of the advantages of explicit cursors is their ability to handle multiple rows. You can fetch rows from the result set one by one or in bulk, depending on your requirements. This allows you to process large result sets efficiently and perform operations on each row individually.

Explicit cursors also provide the flexibility to perform DML operations. You can use them to insert, update, or delete rows in the database. This makes explicit cursors suitable for scenarios where you need to modify data based on certain conditions or perform complex data manipulations.

Another advantage of explicit cursors is that they allow you to control the cursor operations explicitly. You can open the cursor, fetch rows selectively, and close the cursor at specific points in your code. This level of control is beneficial when you need to handle exceptions, perform error handling, or implement custom result set processing logic.

Similarities

While explicit and implicit cursors have their differences, they also share some similarities in terms of functionality and purpose. Both types of cursors are used to retrieve data from the database and process result sets. They allow you to iterate over the rows returned by a query and perform operations on each row.

Both explicit and implicit cursors can be used to fetch rows into variables, allowing you to access and manipulate the data easily. They provide a way to navigate through the result set and retrieve specific columns or values as needed.

Both types of cursors can be used in PL/SQL blocks, stored procedures, and functions. They are an integral part of Oracle's procedural language and provide the necessary tools for data manipulation and processing.

Another similarity between explicit and implicit cursors is that they both require proper error handling. When working with cursors, it is important to handle exceptions and errors that may occur during the execution of SQL statements. This ensures that your code is robust and can handle unexpected situations.

Overall, both explicit and implicit cursors serve the purpose of retrieving and manipulating data from the database. They provide different levels of control and flexibility, allowing developers to choose the appropriate cursor type based on their specific requirements.

Conclusion

In conclusion, explicit and implicit cursors are two types of cursors used in Oracle for result set processing. Implicit cursors are automatically created by Oracle and are suitable for simple queries that involve single-row operations. On the other hand, explicit cursors require explicit declaration and management, providing more control and flexibility for complex queries and DML operations.

Both types of cursors have their advantages and limitations, and the choice between them depends on the specific requirements of your application. Understanding the attributes and differences of explicit and implicit cursors is essential for efficient and effective database programming in Oracle.