How to Create and Manage Temporary Tables in Oracle?

Create and manage temporary tables in Oracle database

In database programming, it is often necessary to create temporary tables to store intermediate data or perform temporary calculations. This article will explore how to create temporary tables in Oracle database.

Method

Unlike SQL Server which uses the DECLARE statement to create temporary tables, Oracle takes a different approach. In Oracle, temporary tables are created similar to normal tables but have additional properties that distinguish them from permanent tables.

To create a temporary table, you can use the following syntax:

<code class="language-sql">CREATE GLOBAL TEMPORARY TABLE 表名 (
  列名1 数据类型,
  列名2 数据类型,
  ...
)
ON COMMIT PRESERVE ROWS;</code>

The

GLOBAL TEMPORARY keyword specifies that the table is a temporary table and is visible to all sessions. The ON COMMIT PRESERVE ROWS clause preserves the data in the table even after the transaction that created it commits.

Example

Consider the following scenario:

<code class="language-sql">CREATE GLOBAL TEMPORARY TABLE orders(
  order_id NUMBER
)
ON COMMIT PRESERVE ROWS;</code>

This statement creates a temporary table named orders, which contains a single column order_id. The data in this table is retained even after the transaction that created it commits.

Advantages of temporary tables

• Data persistence: Temporary tables allow you to store intermediate data across multiple transactions.
• Performance improvements: By caching data in temporary tables, you can improve query performance by avoiding repeated retrieval of data from disk.
• Data Isolation: Temporary tables provide isolation from other sessions, ensuring each session has its own dedicated data set.

Limitations

• Overhead: Creating and managing temporary tables may increase the overhead of database operations.
• Abuse: Overuse of temporary tables can lead to performance issues and data inconsistencies.

Conclusion

Temporary tables provide a useful way to store intermediate data and perform temporary calculations in Oracle database. By understanding their creation, persistence, and limitations, you can effectively utilize temporary tables in your Oracle applications.

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