Hypercharge Oracle SQL with Temporary Tables

For certain types of SQL operations, the creation of intermediate result tables can result in stunning performance improvements. We will discuss how you can use the global temporary tables (GTT) syntax to improve the speed of queries that perform complex summarization activities, and how to speed up two-stage queries that perform both summarization and comparison activities.

Using temporary tables with Dictionary Views

The prudent use of temporary tables can dramatically improve Oracle SQL performance. To illustrate the concept, consider the following example from the DBA world. In the query that follows, we want to identify all users who exist within Oracle who have not been granted a role. We could formulate the query as an anti-join with a noncorrelated subquery (against a complex view) as shown here:

   username NOT IN
      (select grantee from dba_role_privs);

This query runs in 18 seconds. As you may remember from Chapter 12, these anti-joins can often be replaced with an outer join. However, we have another option by using CTAS. Now, we rewrite the same query to utilize temporary tables by selecting the distinct values from each table.

Please read these important notes on SQL tuning with temporary tables:



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How do I do that in Oracle?

Explore this series for a collection of tips that explain in detail how to perform specific tasks in Oracle related to database administration. Consisting of expert advice from top Oracle gurus, these how-tos provide step-by-step instructions to guide you through database administration processes related to installation and upgrades, backup and recovery and other Oracle basics.