Updating multiple tables in oracle
When a session is created, it is automatically mapped to a consumer group based on mapping rules that you set up.
As a database administrator (DBA), you can manually switch a session to a different consumer group.
See "The Types of Resources Managed by the Resource Manager" for more information.
The resource allocation scheme then works like this: The resource plan (the currently active plan) divides resources among consumer groups and subplans.
Each subplan allocates its portion of the total resource allocation among its consumer groups and subplans.
If you will not use all of the rows in the staging table, you can filter the DELETE and INSERT statements by using a WHERE clause to leave out rows that are not actually changing.
However, if most of the rows in the staging table will not participate in the merge, we recommend performing an UPDATE and an INSERT in separate steps, as described later in this section.