Purpose of Temporary Tables

Temporary tables are useful in applications where a result set must be buffered.

For example, a scheduling application enables college students to create optional semester course schedules. A row in a global temporary table represents each schedule. During the session, the schedule data is private. When the student chooses a schedule, the application moves the row for the chosen schedule to a permanent table. At the end of the session, the database automatically drops the schedule data that was in the global temporary table.

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Private temporary tables are useful for dynamic reporting applications. For example, a customer resource management (CRM) application might connect as the same user indefinitely, with multiple sessions active at the same time. Each session creates a private temporary table named ORA$PTT_crm for each new transaction. The application can use the same table name for every session, but change the definition. The data and definition are visible only to the session. The table definition persists until the transaction ends or the table is manually dropped.

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Segment Allocation in Temporary Tables

Like permanent tables, global temporary tables are persistent objects that are statically defined in the data dictionary. For private temporary tables, metadata exists only in memory, but can reside in the temporary tablespace on disk.

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For global and private temporary tables, the database allocates temporary segments when a session first inserts data. Until data is loaded in a session, the table appears empty. For transaction-specific temporary tables, the database deallocates temporary segments at the end of the transaction. For session-specific temporary tables, the database deallocates temporary segments at the end of the session.

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