Temporary Tables in Oracle SQL

Temporary tables in Oracle SQL are used to store data temporarily for the duration of a session or a transaction. They are particularly useful for storing intermediate results or for managing large datasets that need to be processed in stages. Understanding temporary tables can significantly enhance your ability to manage complex data operations efficiently.

1. Session-Specific Temporary Tables

Session-specific temporary tables are created with the GLOBAL TEMPORARY clause and are visible only to the session that created them. Data stored in these tables is automatically deleted when the session ends. This makes them ideal for storing data that is only needed for the duration of a user session.

Example:

Suppose you are developing a web application where users need to perform complex calculations. You can use a session-specific temporary table to store intermediate results:

CREATE GLOBAL TEMPORARY TABLE temp_calculations (
    calculation_id NUMBER,
    result NUMBER
) ON COMMIT PRESERVE ROWS;

In this example, the temp_calculations table will store data only for the duration of the user's session, and the data will be automatically cleared when the session ends.

2. Transaction-Specific Temporary Tables

Transaction-specific temporary tables are also created with the GLOBAL TEMPORARY clause but are visible only for the duration of a transaction. Data stored in these tables is automatically deleted when the transaction is committed or rolled back. This makes them suitable for storing data that is only needed for the duration of a single transaction.

Example:

Consider a financial application where you need to perform a series of calculations within a single transaction. You can use a transaction-specific temporary table to store intermediate results:

CREATE GLOBAL TEMPORARY TABLE temp_transaction_data (
    transaction_id NUMBER,
    amount NUMBER
) ON COMMIT DELETE ROWS;

In this example, the temp_transaction_data table will store data only for the duration of the transaction, and the data will be automatically cleared when the transaction is committed or rolled back.

3. Temporary Tables vs. Regular Tables

While regular tables are permanent and store data across sessions and transactions, temporary tables are designed for temporary data storage. Regular tables are suitable for long-term data storage and retrieval, while temporary tables are ideal for intermediate data processing and temporary data storage.

Example:

Imagine you are managing a large dataset that needs to be processed in multiple stages. You can use a combination of regular and temporary tables to manage the data efficiently:

CREATE TABLE permanent_data (
    data_id NUMBER,
    data_value VARCHAR2(100)
);

CREATE GLOBAL TEMPORARY TABLE temp_processing_data (
    data_id NUMBER,
    processed_value VARCHAR2(100)
) ON COMMIT PRESERVE ROWS;

In this example, the permanent_data table stores the original dataset, while the temp_processing_data table stores intermediate processing results that are only needed for the duration of the session.

Understanding and utilizing temporary tables effectively can significantly enhance your ability to manage complex data operations in Oracle SQL. By leveraging session-specific and transaction-specific temporary tables, you can optimize data processing and ensure efficient use of database resources.