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。1、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;2、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;3、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');4、序列号
查看序列号，last_number是当前值
SQL>select * from user_sequences;5、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');6、同义词
查看同义词的名称
SQL>select * from user_synonyms;7、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;8、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'); 三、查看数据库的SQL1、查看表空间的名称及大小select t.tablespace_name, round(sum(bytes/(1024*1024)),0) ts_size
from dba_tablespaces t, dba_data_files d where t.tablespace_name = d.tablespace_name group by t.tablespace_name;2、查看表空间物理文件的名称及大小
select tablespace_name, file_id, file_name,
round(bytes/(1024*1024),0) total_space from dba_data_files order by tablespace_name;3、查看回滚段名称及大小
select segment_name, tablespace_name, r.status,
(initial_extent/1024) InitialExtent,(next_extent/1024) NextExtent, max_extents, v.curext CurExtent From dba_rollback_segs r, v$rollstat v Where r.segment_id = v.usn(+) order by segment_name ;4、查看控制文件
select name from v$controlfile;
5、查看日志文件
select member from v$logfile;
6、查看表空间的使用情况
select sum(bytes)/(1024*1024) as free_space,tablespace_name
from dba_free_space group by tablespace_name;SELECT A.TABLESPACE_NAME,A.BYTES TOTAL,B.BYTES USED, C.BYTES FREE,
(B.BYTES*100)/A.BYTES "% USED",(C.BYTES*100)/A.BYTES "% FREE" FROM SYS.SM$TS_AVAIL A,SYS.SM$TS_USED B,SYS.SM$TS_FREE C WHERE A.TABLESPACE_NAME=B.TABLESPACE_NAME AND A.TABLESPACE_NAME=C.TABLESPACE_NAME;7、查看数据库库对象
select owner, object_type, status, count(*) count# from all_objects group by owner, object_type, status;
8、查看数据库的版本
Select version FROM Product_component_version
Where SUBSTR(PRODUCT,1,6)='Oracle';9、查看数据库的创建日期和归档方式
Select Created, Log_Mode, Log_Mode From V$Database;
四、ORACLE用户连接的管理用系统管理员，查看当前数据库有几个用户连接：
SQL> select username,sid,serial# from v$session;
如果要停某个连接用
SQL> alter system kill session 'sid,serial#';
如果这命令不行,找它UNIX的进程数
SQL> select pro.spid from v$session ses,v$process pro where ses.sid=21 and ses.paddr=pro.addr;
说明：21是某个连接的sid数
然后用 kill 命令杀此进程号。