基于函数的索引可以是 B-tree 索引或位图索引。 用于构建索引的函数可以是算术表达式,也可以是包含 SQL 函数、用户定义的 PL/SQL 函数、包函数或 C 调用的表达式。例如,一个函数可以将两列的值相加。 3.1.4.1. 基于函数的索引的用途 基于函数的索引对于评估包含函数的 WHERE 子句中的语句非常有效。数据库只在查...
Hierarchical queries return data in a tree like structure. The query is performed by walking the tree that is made up of parents and children, each non-root-node linked to a parent node. A common example of a hierarchical query is the one involving Employees who are linked to each other ...
Row operators return or reference particular rows.ALLretains duplicate rows in the result of a query or in an aggregate expression.DISTINCTeliminates duplicate rows from the result of a query or from an aggregate expression.PRIORrefers to the parent row of the current row returned by a tree-str...
This asset includes a PL/SQL query that hits Oracle system tables and provides a count of objects by schema type, object type, and status. It also provides a rough estimate of raw data in each schema and the sizing of tables in each schema, with results stored in a CSV format. Autom...
A view is an Oracle data structure defined through a SQL statement. The SQL statement is stored in the database. When you use a view in a query, the stored query is executed and the base table data is returned to the user. Views do not contain data, but represent ways to look at ...
A cluster node with a large document set can be categorized into child cluster nodes, and a hierarchy cluster result tree is built. Users can navigate directly to a specific cluster node or refine their query by combining the original query and cluster results. See Also: ■ Oracle SES ...
(我们称之为soft closed session cursor),这么做的目的是很明显的,因为这个soft closed掉的sessioncursor已经和包含其执行计划和parse tree的sharedcursor建立了联系,那么当在这个session中再次执行同样的sql的时候,Oracle就不再需要去扫描library cache了,直接把刚才已经soft closed掉的session cursor拿过来用就好了,这就...
The Ora2Pg tool connects your Oracle database, scans it automatically, and extracts its structure or data. Then Ora2Pg generates SQL scripts that you can load into your PostgreSQL database. You can use Ora2Pg for tasks such as reverse-engineering an Oracle database, migrating a huge ...
Oracle Globally Distributed Database is a comprehensive database solution, providing efficient data model and schema management, powerful query language and SQL capabilities, advanced indexing and data organization, support for complex data types, stored procedures, and triggers. It delivers high performan...
Ora2Pg is a free tool used to migrate an Oracle database to a PostgreSQL compatible schema. It connects your Oracle database, scan it automatically and extracts its structure or data, it then generates SQL scripts that you can load into PostgreSQL. - dar