Prefix	Scope
USER	can view only what is in USER’s scheme (generally exclude column OWNER)
ALL	Can view everything that the user can access
DBA	Can view everything what maximum any user can access

USER Views

The views with the prefix USER generally refer to views that contain data about a particular user’s own object, which includes data about objects created by that user, grants made by that user, and so on.

It is generally a subset of ALL_views. It has only data related to the user and has columns similar to other views.

Examples:

Some Common Views with the prefix USER are:

USER_OBJECTS - view that contains data about all objects
(tables, views, indexes, procedures, and functions, etc.) owned by that particular user
USER_TAB_COLUMNS - view that contains data about the columns of all 
tables and views owned by that particular user.
USER_TABLES - view that contains data about all tables owned by that particular user.
USER_VIEWS - view that contains data about all views owned by that particular user.
USER_CONSTRAINTS - view that contains data about all constraints 
(primary keys, foreign keys, and unique constraints, etc.) owned by the particular user.
USER_SEQUENCES - view that contains data about all 
sequences owned by that particular user.
USER_TRIGGERS - view that contains data about all triggers 
owned by that particular user.
USER_INDEXES - view that contains data about all indexes owned by that particular user.
USER_SYNONYMS - view that contains data about all synonyms owned by that particular user.
USER_TAB_COMMENTS - view that contains comments on tables and views owned by that particular user.

Example Query To Access the Views

Query to print all the objects (name and type) in a user’s scheme

Syntax:

SELECT object_name, object_type FROM user_objects; 

Query to print all the data about all Tables owned by the user:

SELECT * FROM user_tables;

ALL Views

Views with the prefix ALL are views that contain data about not only objects owned by the user but also objects with access via public or explicit grants of privileges or roles.

Examples:

Some Common Views with the prefix ALL are:

ALL_OBJECTS - views that contains data about all objects (tables, views, indexes, procedures, etc..) in the database
ALL_TAB_COLUMNS - views that contains data about all columns in all the tables and views in the database
ALL_TABLES - views that contains data about all tables and views in the database
ALL_VIEWS - views that contains data about all views in the database in the database
ALL_USERS - Views that contains data about data about all users in the database
ALL_CONSTRAINTS - Views that contains data about all constraints 
(primary keys, foreign keys, unique constraints, etc. ) in the database
ALL_SEQUENCES - View that contains data about all sequences in the database
ALL_INDEXES - Views that contains data about all indexes in the database
ALL_TRIGGERS - Views that contains data about about all triggers in the database
ALL_INDEXES: View that contains data about all indexes in the database.
ALL_SYNONYMS - Views that contains data about all synonyms in the database

Example:

Query to print all the objects (name and type) to which the user has access:

SELECT owner, object_name, object_type FROM all_objects; 

Query to print all the data about all Tables to which the user has access:

SELECT * FROM all_views;

DBA Views

Views with the prefix DBA are views that are generally accessed only by the Database Administrators or any user who has got the system privilege SELECT ANY TABLE. It will have access to the OWNER column as well. The prefix is generally SYS followed by the table name.

The views are similar to the ALL and USER views

Example:

Query to print all the objects (name and type) in the DataBase:

SELECT owner, object_name, object_type FROM sys.dba_objects;

FAQs on Data Dictionary Tables in RDMS

1. How can you ensure the data dictionary tables themselves remain consistent and accurate over time, especially in large, dynamic databases?

Maintaining data dictionary tables’ accuracy and consistency is crucial. This is typically done through automated processes, triggers, and regular integrity checks. Tools like version control systems can help track changes and rollbacks.

2. In a distributed database environment, how do you manage the data dictionary tables to ensure synchronization and coherence across different nodes or instances?

In a distributed environment, maintaining consistency across data dictionary tables can be challenging. Distributed database management systems employ techniques like two-phase commits, distributed locks, and synchronization protocols to ensure data dictionary tables remain coherent.

3. What are the potential security risks associated with data dictionary tables, and how can these risks be mitigated?

Data dictionary tables contain critical metadata. Unauthorized access can lead to security breaches. Implementing strict access controls, encryption, and auditing mechanisms can help mitigate these risks. Regular security audits are also essential.

4. How do you handle versioning and historical data in data dictionary tables, especially when schema changes occur frequently?

Managing historical data in data dictionary tables often involves creating historical snapshots or audit trails. This requires careful planning, triggers to capture changes, and additional tables to store historical versions of metadata.