The CAT view lists the objects in the current schema.
The following code shows an example of using the CAT view.
select * from cat;
To know more about a specific data dictionary view, use command DESCRIBE or query the data dictionary view DICT_COLUMNS.
describe ALL_USERS Name Null? Type USERNAME NOT NULL VARCHAR2(30) USER_ID NOT NULL NUMBER CREATED NOT NULL DATE select column_name, comments from dict_columns where table_name = 'ALL_USERS';
The following code shows a query against the NLS_SESSION_PARAMETERS view (NLS stands for National Language Support).
The result shows, for example, the NLS_DATE_FORMAT value used to display dates.
SQL> SQL> select * from nls_session_parameters; PARAMETER-- w w w . j a v a2 s . com -------------------------------------------------------------------------------- VALUE -------------------------------------------------------------------------------- NLS_LANGUAGE AMERICAN NLS_TERRITORY AMERICA
The following table lists a selection of useful Oracle data dictionary tables.
| View | Description |
|---|---|
| DICTIONARY | Description of the data dictionary itself |
| DICT_COLUMNS | Data dictionary column descriptions |
| ALL_USERS | Information about all database users |
| ALL_INDEXES1 | All indexes |
| ALL_SEQUENCES1 | All sequences |
| ALL_OBJECTS1 | All objects |
| ALL_SYNONYMS1 | All synonyms |
| ALL_TABLES1 | All tables |
| ALL_VIEWS1 | All views |
| USER_INDEXES2 | Indexes |
| USER_SEQUENCES2 | Sequences |
| USER_OBJECTS2 | Objects |
| USER_SYNONYMS2 | Synonyms |
| USER_TABLES2 | Tables |
| USER_TAB_COLUMNS2 | Columns |
| USER_VIEWS2 | Views |
| USER_RECYCLEBIN | Dropped objects |
| CAT | Synonym for USER_CATALOG |
| COLS | Synonym for USER_TAB_COLUMNS |
| DICT | Synonym for DICTIONARY |
| DUAL | Dummy table, with one row and one column |
| IND | Synonym for USER_INDEXES |
| OBJ | Synonym for USER_OBJECTS |
| SYN | Synonym for USER_SYNONYMS |
| TABS | Synonym for USER_TABLES |