052-236(新增70题2018)

The customer and order tables are often used in joins, thereby resulting in complex queries. You created views to simplify the writing of queries.

These views are stored in _____.

A. user tables

B. view segment

C. table segment

D. data dictionary

E. object segment

F. performance tables

Answer: D

• Contents of the Data Dictionary

The data dictionary consists of the following types of objects:

• Base tables

  These underlying tables store information about the database. Only Oracle Database should write to and read these tables. Users rarely access the base tables directly because they are normalized and most data is stored in a cryptic format.

• Views

  These views decode the base table data into useful information, such as user or table names, using joins and WHERE clauses to simplify the information. These views contain the names and description of all objects in the data dictionary. Some views are accessible to all database users, whereas others are intended for administrators only.

Typically, data dictionary views are grouped in sets. In many cases, a set consists of three views containing similar information and distinguished from each other by their prefixes, as shown in Table 6-1. By querying the appropriate views, you can access only the information relevant for you.

转载于:https://www.cnblogs.com/Babylon/p/8622535.html