13. Hierarchy-related operations
This type of operation is related to SQL statements that contain hierarchical operations. The so-called hierarchy means that the data in the operation-related database objects has a parent-child or superior-subordinate relationship. Depending on the specific SQL statement and other related factors, the following operations may appear in the execution plan of the relevant SQL statement.
1）CONNECT BY
When performing hierarchical data retrieval, perform a hierarchical self-join.
--Note:
1) Starting from Oracle version 9.0, this operation is no longer the default behavior of hierarchical query statements. To make this operation appear in the execution plan, the parameter "_old_connect_by_enabled" needs to be set to true. In Oracle version 11.2.0, this parameter defaults to false.
This operation is specifically shown in node 1 in Figure 13-1. </