SQL> desc dictionary; 名称 空值? 类型 ----------------------------------------------------- -------- ------------------------------------ TABLE_NAME VARCHAR2(30) COMMENTS VARCHAR2(4000)SQL> select * from dictionary where rownum<10;TABLE_NAME ------------------------------ COMMENTS ---------------------------------------------------------------------------------------------------- ALL_ALL_TABLES Description of all object and relational tables accessible to the userALL_ARGUMENTS Arguments in object accessible to the userALL_CATALOG All tables, views, synonyms, sequences accessible to the userALL_CLUSTERS Description of clusters accessible to the userALL_CLUSTER_HASH_EXPRESSIONS Hash functions for all accessible clustersALL_COLL_TYPES Description of named collection types accessible to the userALL_COL_COMMENTSTABLE_NAME ------------------------------ COMMENTS ---------------------------------------------------------------------------------------------------- Comments on columns of accessible tables and viewsALL_COL_PRIVS Grants on columns for which the user is the grantor, grantee, owner, or an enabled role or PUBLIC is the granteeALL_COL_PRIVS_MADE Grants on columns for which the user is owner or grantor 已选择9行。
名称 空值? 类型
----------------------------------------------------- -------- ------------------------------------
TABLE_NAME VARCHAR2(30)
COMMENTS VARCHAR2(4000)SQL> select * from dictionary where rownum<10;TABLE_NAME
------------------------------
COMMENTS
----------------------------------------------------------------------------------------------------
ALL_ALL_TABLES
Description of all object and relational tables accessible to the userALL_ARGUMENTS
Arguments in object accessible to the userALL_CATALOG
All tables, views, synonyms, sequences accessible to the userALL_CLUSTERS
Description of clusters accessible to the userALL_CLUSTER_HASH_EXPRESSIONS
Hash functions for all accessible clustersALL_COLL_TYPES
Description of named collection types accessible to the userALL_COL_COMMENTSTABLE_NAME
------------------------------
COMMENTS
----------------------------------------------------------------------------------------------------
Comments on columns of accessible tables and viewsALL_COL_PRIVS
Grants on columns for which the user is the grantor, grantee, owner,
or an enabled role or PUBLIC is the granteeALL_COL_PRIVS_MADE
Grants on columns for which the user is owner or grantor
已选择9行。
数据字典中包括下列信息的描述:
(1) ORACLE所有用户的标识及用户的存取权限。
(2) 每个用户所拥有的数据库实体(表、空间定义、视图、索引、聚簇和同义词)的定义。
(3) 为数据库实体分配的空间情况。
我们可以通过查询语句查看数据字典中的有关内容。例如:用户需要查看当前用户创建的所有基表、视图和同义词清单,可以使用下列命令:
SQL>SELECT * FROM CAT;
CAT表中存放的就是有关用户创建的基表、视图和同义词情况的描述。
数据字典由几个基础表及派生出来的视图组成。基础表是由ORACLE RDBMS自动更新,用户基本上不访问基础表,ORACLE RDBMS不断地更新数据字典的基础表,而视图总是引用基础表中的最新数据。
一般来说,用户不能直接更新ORACLE的数据字典,因为用户操作不当、删除或修改了某些数据字典的内容,就会造成数据库的破坏。