dictionary全部数据字典表的名称和解释，它有一个同义词dict    dict_column

全部数据字典表里字段名称和解释：

如果我们想查询跟索引有关的数据字典时，可以用下面这条SQL语句:
        SQL>select * from dictionary where instr(comments,'index')>0;       
如果我们想知道user_indexes表各字段名称的详细含义，可以用下面这条SQL语句:
        SQL>select column_name,comments from dict_columns where table_name='USER_INDEXES';       
依此类推，就可以轻松知道数据字典的详细名称和解释，不用查看ORACLE的其它文档资料了。

下面按类别列出一些ORACLE用户常用数据字典的查询使用方法。
一、用户
        查看当前用户的缺省表空间     SQL>select username,default_tablespace from user_users;
        查看当前用户的角色  SQL>select * from user_role_privs;
        查看当前用户的系统权限和表级权限 SQL>select * from user_sys_privs;SQL>select * from user_tab_privs;
二、表       
        查看用户下所有的表    SQL>select * from user_tables;           
        查看名称包含log字符的表    SQL>select object_name,object_id from user_objects         where instr(object_name,'LOG')>0;  
        查看某表的创建时间     SQL>select object_name,created from user_objects where object_name=upper('&table_name');       
        查看某表的大小    SQL>select sum(bytes)/(1024*1024) as "size(M)" from user_segments
                                              where segment_name=upper('&table_name');       
        查看放在ORACLE的内存区里的表    SQL>select table_name,cache from user_tables where instr(cache,'Y')>0;      
三、索引       
        查看索引个数和类别    SQL>select index_name,index_type,table_name from user_indexes order by table_name;       
        查看索引被索引的字段    SQL>select * from user_ind_columns where index_name=upper('&index_name');       
        查看索引的大小    SQL>select sum(bytes)/(1024*1024) as "size(M)" from user_segments         where segment_name=upper('&index_name');       
四、序列号       
        查看序列号，last_number是当前值    SQL>select * from user_sequences;       
五、视图       
        查看视图的名称    SQL>select view_name from user_views;       
        查看创建视图的select语句    SQL>set view_name,text_length from user_views;    SQL>set long 2000;说明：可以根据视图的text_length值设定set long 的大小    SQL>select text from user_views where view_name=upper('&view_name');      
 六、同义词       
         查看同义词的名称    SQL>select * from user_synonyms;       
 七、约束条件       
         查看某表的约束条件   
         SQL>select constraint_name, constraint_type,search_condition, r_constraint_name
                 from user_constraints where table_name = upper('&table_name');
        SQL>select c.constraint_name,c.constraint_type,cc.column_name     
                from user_constraints c,user_cons_columns cc   
                where c.owner = upper('&table_owner')
                and c.table_name = upper('&table_name')   
                and c.owner = cc.owner
                and c.constraint_name = cc.constraint_name   
                order by cc.position;               
八、存储函数和过程       
        查看函数和过程的状态   
                SQL>select object_name,status from user_objects where object_type='FUNCTION';   
                SQL>select object_name,status from user_objects where object_type='PROCEDURE';       
        查看函数和过程的源代码    SQL>select text from all_source where owner=user and name=upper('&plsql_name');       
九、触发器       
        查看触发器   
                set long 50000;   
                set heading off;   
                set pagesize 2000;   
                select    'create or replace trigger "' || trigger_name || '"' || chr(10)||     decode( substr( trigger_type, 1, 1 ),             'A', 'AFTER', 'B', 'BEFORE', 'I', 'INSTEAD OF' ) ||                  chr(10) ||     triggering_event || chr(10) ||     'ON "' || table_owner || '"."' ||           table_name || '"' || chr(10) ||     decode( instr( trigger_type, 'EACH ROW' ), 0, null,                'FOR EACH ROW' ) || chr(10) ,     trigger_body    from user_triggers;