How Do I Create and Manage Temporary Tables in Oracle Databases?

Managing Temporary Data in Oracle: A Guide to Temporary Tables

Oracle databases offer temporary tables as a mechanism for managing temporary datasets within a session. Unlike some other database systems, in Oracle only the data within the temporary table is transient; the table structure itself persists as a regular database object.

Creating Global Temporary Tables

The standard approach involves CREATE GLOBAL TEMPORARY TABLE. This creates a temporary table accessible only within the current session.

Syntax:

<code class="language-sql">CREATE GLOBAL TEMPORARY TABLE table_name (column_definition)
ON COMMIT {PRESERVE ROWS | DELETE ROWS}</code>

• ON COMMIT PRESERVE ROWS: Data persists across transaction commits.
• ON COMMIT DELETE ROWS: Data is removed upon transaction completion.

Example:

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

Leveraging Oracle 18c Private Temporary Tables

Oracle 18c introduced private temporary tables, providing session-specific, in-memory storage. These tables are created and dropped dynamically within a single session.

Syntax:

<code class="language-sql">CREATE PRIVATE TEMPORARY TABLE table_name AS SELECT * FROM existing_table;</code>

Example:

<code class="language-sql">CREATE PRIVATE TEMPORARY TABLE my_temp_sales AS
SELECT * FROM sales WHERE sale_date = SYSDATE;</code>

Important Considerations:

While convenient, overuse of temporary tables should be avoided. In many cases, inline views offer a more efficient alternative by streamlining multiple SQL statements into a single query. Careful consideration of performance implications is crucial when working with temporary tables in Oracle.

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