1. 查询系统所有对象
select owner, object_name, object_type, created, last_ddl_time, timestamp, status
from dba_objects
where owner=upper('scott')

2. 查看系统所有表
select owner, table_name, tablespace_name from dba_tables

3. 查看所有用户的表
select owner, table_name, tablespace_name from all_tables

4. 查看当前用户表
select table_name, tablespace_name from user_tables

5. 查看用户表索引
select t.*,i.index_type from user_ind_columns t, user_indexes i where
t.index_name = i.index_name and t.table_name = i.table_name
and t.table_name = 要查询的表

6. 查看主键
select cu.* from user_cons_columns cu, user_constraints au
where cu.constraint_name = au.constraint_name
and au.constraint_type = upper('p') and au.table_name = 要查询的表

7. 查看唯一性约束
select column_name from user_cons_columns cu, user_constraints au
where cu.constraint_name = au.constraint_name and au.constraint_type =? upper('u')
and au.table_name = 要查询的表

8. 查看外键
select * from user_constraints c where c.constraint_type = 'r' and c.table_name = 要查询的表
select * from user_cons_columns cl where cl.constraint_name = 外键名称
select * from user_cons_columns cl where cl.constraint_name = 外键引用表的键名

9. 查看表的列属性
select t.*,c.comments
from user_tab_columns t, user_col_comments c
where t.table_name = c.table_name and t.column_name = c.column_name and t.table_name = 要查询的表

10. 查看所有表空间
select tablespace_name from dba_data_files group by tablespace_name

############################################
11. 查看oracle最大连接数
sql>show parameter processes??? #最大连接数

12. 修改最大连接数
sql>alter system set processes=value scope=spfile
–重启数据库
sql>shutdown force
sql>start force

13. 查看当前连接数
sql>select * from v$session where username is not null

14. 查看不同用户的连接数
sql>select username,count(username) from v$session where username is not null group by username #查看指定用户的连接数

15. 查看活动的连接数
sql>select count(*) from v$session where status='active' #查看并发连接数

16. 查看指定程序的连接数
sql>select count(*) from v$session where program='jdbc thin client' #查看jdbc连接oracle的数目

17. 查看数据库安装实例(dba权限)
sql>select * from v$instance

18. 查看运行实例名
sql>show parameter instance_name

19. 查看数据库名
sql>show parameter db_name

20. 查看数据库域名
sql>show parameter db_domain

21. 查看数据库服务名
sql>show parameter service_names

22. 查看全局数据库名
sql>show parameter global

23. 查看表空间使用率

-- (1)

select dbf.tablespace_name,

       dbf.totalspace "总量(m)",

       dbf.totalblocks as "总块数",

       dfs.freespace "剩余总量(m)",

       dfs.freeblocks "剩余块数",

       (dfs.freespace / dbf.totalspace) * 100 as "空闲比例"

  from (select t.tablespace_name,

               sum(t.bytes) / 1024 / 1024 totalspace,

               sum(t.blocks) totalblocks

          from dba_data_files t

         group by t.tablespace_name) dbf,

       (select tt.tablespace_name,

               sum(tt.bytes) / 1024 / 1024 freespace,

               sum(tt.blocks) freeblocks

          from dba_free_space tt

         group by tt.tablespace_name) dfs

 where trim(dbf.tablespace_name) = trim(dfs.tablespace_name)

-- (2)

select t.name "tablespace name",

       free_space,

       (total_space - free_space) used_space,

       total_space

  from (select tablespace_name, sum(bytes / 1024 / 1024) free_space

          from sys.dba_free_space

         group by tablespace_name)