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Discover how to create a temporary table in Oracle, tailored for Sybase developers. Learn the best practices and techniques for handling temporary data effectively.
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How to Create a Temporary Table in Oracle: A Guide for Sybase Developers

As a developer transitioning from Sybase or SQL Server to Oracle, you might be accustomed to creating temporary tables in a straightforward manner, using syntax such as:

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In this context, #temp exists for the duration of the session and is localized to your user. However, in Oracle, the terminology and approach can differ significantly. Here, we’ll clarify the concept of temporary tables in Oracle and provide you with effective solutions to achieve similar functionality.

Understanding Temporary Tables in Oracle

In Oracle, the term "temporary table" refers to Global Temporary Tables (GTT). Although they serve a similar purpose as temporary tables in Sybase, they have unique characteristics:

Global Temporary Tables exist in the database schema, but the data they hold is session-specific and can be seen by different sessions, though only the data inserted by the specific session is accessible to that session.

The table structure is persistent, but the data is temporary, either stored for the session or for the transaction, depending on how you define it.

Creating and Using Temporary Tables in Oracle

Using a Direct Query:
If you are working with a simple dataset, you might want to execute your queries in one shot without creating a traditional temporary table. Here’s how you can achieve that:

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This method pulls the results you need directly from the database without the extra step of materializing them into a temporary table.

Subquery Factoring with Materialize Hint:
For more complex scenarios or larger datasets, consider using the Subquery Factoring Clause (also known as Common Table Expression, CTE). You can include a materialization hint to enhance performance:

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This technique allows you to define a temporary dataset that can be referenced throughout the execution of your query, much like how you would use a temporary table in Sybase.

Using Global Temporary Tables:
If the above approaches do not meet your needs, you may opt for a Global Temporary Table:

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ON COMMIT DELETE ROWS: Data gets deleted at the end of each transaction.

ON COMMIT PRESERVE ROWS: Data persists for the duration of the session.

After creating the GTT, you can insert your data similarly:

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Then, simply query your GTT as needed for your application.

Conclusion

Transitioning to Oracle from Sybase can feel challenging, especially when dealing with temporary data. However, with the methods outlined above, you can efficiently create and utilize temporary tables in Oracle just like you would in Sybase. Whether you choose to use a direct query, a subquery factoring clause, or a Global Temporary Table, Oracle offers various options to help manage temporary datasets effectively.

By mastering these techniques, you can ensure that your workflows remain seamless despite the differences between database systems. Happy querying!