SQL语言基础-查询数据字典

查询数据字典 * 查看用户所拥有的数据类型. 查看用户拥有的表、视图、同义词、序列. SQL> SELECT * 2 FROM user_tables; SQL> SELECT DISTINCT object_type 2 FROM user_objects; SQL> SELECT * 2 FROM user_catalog; 描述用户拥有的表. * Querying the Data Dictionary You can query the data dictionary tables to view various database objects owned by you. The data dictionary tables frequently used are these: USER_TABLES USER_OBJECTS USER_CATALOG Note: USER_CATALOG has a synonym called CAT. You can use this synonym instead of USER_CATALOG in SQL statements. SQL> SELECT * 2 FROM CAT; Instructor Note (for page 10-11) Explain the things to consider when declaring a column as LONG datatype: A LONG column is not copied when a table is created using a subquery. A LONG column cannot be included in a GROUP BY or an ORDER BY clause. Only one LONG column is allowed per table. No constraints can be defined on a LONG column.