Oracle Views

An Oracle database consists of a vast amount of underlying metadata that stores information about the database itself. This metadata is extremely cryptic and as such Oracle have provided ‘user friendly’ views to enable the user or DBA to view this data in a meaningful format.

There are two types of Oracle Views:

Data Dictionary Views
Dynamic Performance Views

Data Dictionary Views begin with DBA_ , USER_ or ALL_ . The difference is as follows: DBA_ Views show information on all the tables in the database, ALL_ shows information on all the tables that you own or have been granted access to. USER_ shows information on all the tables that you own.

There are some differences between Data Dictionary Views and Dynamic Performance Views:

Data Dictionary Views usually have plural names (DBA_TABLES), Dynamic Performance Views, singular (V$DATAFILE)
Data Dictionary Views are only available whilst the database is open, some V$ Views are available when the DB is not fully open
The data in Data Dictionary Views is usually UPPERCASE whilst V$ data is usually lowercase
The data in Data Dictionary Views is static and not cleared when the DB is restarted, V$ data is cleared after a restart

Examples of Data Dictionary Views

DBA_TABLES
DBA_TABLESPACES
DBA_USERS
DBA_VIEWS

Examples of Dynamic Performance Views

V$VERSION
V$OPTION
V$DATABASE
V$SQL

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