Data dictionary tables are not directly accessible, but you can access information in them through data dictionary views. To list the data dictionary views available to you, query the viewDICTIONARY.
Many data dictionary tables have three corresponding views:
AnALL_view displays all the information accessible to the current user, including information from the current user's schema as well as information from objects in other schemas, if the current user has access to those objects by way of grants of privileges or roles.
ADBA_view displays all relevant information in the entire database.DBA_views are intended only for administrators. They can be accessed only by users with theSELECT ANY DICTIONARYprivilege. This privilege is assigned to theDBArole when the system is initially installed.
AUSER_view displays all the information from the schema of the current user. No special privileges are required to query these views.
The columns of theALL_,DBA_, andUSER_views corresponding to a single data dictionary table are usually nearly identical. Therefore, these views are described in full only once in this chapter, at their first occurrence alphabetically, and are listed without full descriptions at their other occurrences.动态性能视图
This part describes the dynamic performance views, which are often referred to as V$ views. This part contains the following chapters: