oracle如何查看当前有哪些用户连接到数据库

可以执行以下语句：
SELEct user@R_419_6889@,serial#,sID from v$session; ---查询用户会话
alter system kill session ‘serial#,sID ‘;---删除相关用户会话

建议以后台登陆删除用户会话
1、查询Oracle的连接数
SELEct count(*) from v$session;
2、查询Oracle的并发连接数
SELEct count(*) from v$session where status=‘ACTIVE‘;
3、查看不同用户的连接数
SELEct user@R_419_6889@,count(user@R_419_6889@) from v$session where user@R_419_6889@ is not null group by user@R_419_6889@;
4、查看所有用户：
select * from all_users;
5、查看用户或角色系统权限(直接赋值给用户或角色的系统权限)：
SELEct * from dba_sys_privs;
SELEct * from user_sys_privs;
6、查看角色(只能查看登陆用户拥有的角色)所包含的权限
SELEct * from role_sys_privs;
7、查看用户对象权限：
SELEct * from dba_tab_privs;
select * from all_tab_privs;
SELEct * from user_tab_privs;
8、查看所有角色：
SELEct * from dba_roles;
9、查看用户或角色所拥有的角色：
SELEct * from dba_role_privs;
SELEct * from user_role_privs;
10、查看哪些用户有sysdba或sysoper系统权限(查询时需要相应权限)
SELEct * from v$PWfile_USERS;

修改数据库允许的最大连接数：
alter system set processes = 300 scope = spfile;

查看游标数量
SELEct * from v$open_cursor Where user_@R_419_6889@=‘‘

查询数据库允许的最大连接数：
SELEct value from v$parameter where @R_419_6889@ = ‘processes‘;
或者：show parameter processes;

查询数据库允许的最大游标数：
SELEct value from v$parameter where @R_419_6889@ = ‘open_cursors‘

查看Oracle版本
SELEct bAnner from sys.v_$version;

按降序显示用户"SYstem"为每个会话打开的游标数
SELEct o.sID,osuser,machine,count(*) num_curs from v$open_cursor o,v$session s where user_@R_419_6889@ = ‘SYstem‘ and o.sID=s.sid group by o.sID,machine order by num_curs desc;

以上转载自 @R_696_10107@s://www.cnblogs.com/caogang/p/4546072.HTML

保留两位小数以GB为单位显示数据文件大小
SELECT round(SUM(BYTES)/1024/1024/1024,2)||‘GB‘ FROM DBA_DATA_fileS;

以MB为单位表空间分组显示数据文件大小
SELECT tableSPACE_@R_419_6889@,SUM(BYTES)/1024/1024 AS MB FROM DBA_DATA_fileS
GROUP BY tableSPACE_@R_419_6889@;

显示数据库中临时文件的大小
SELECT SUM(BYTES)/1024/1024/1024 AS GB FROM DBA_TEMP_fileS;

显示数据库中日志文件的大小
SELECT SUM(BYTES)/1024/1024/1024 AS GB FROM v$LOG;

显示数据库中数据文件、临时文件、日志文件的总大小
SELECT SUM(GB) AS GB
FROM(
SELECT SUM(BYTES)/1024/1024/1024 AS GB
FROM DBA_DATA_fileS
union all
SELECT SUM(BYTES)/1024/1024/1024
FROM DBA_TEMP_fileS
union all
SELECT SUM(BYTES)/1024/1024/1024
FROM v$LOG
);

SELECT round(SUM(BYTES) / 1024 / 1024,2) "USED(M)"
FROM DBA_SEGMENTS
GROUP BY owneR,tableSPACE_@R_419_6889@
ORDER BY SUM(BYTES) DESc;

--1、查看所有表空间及表空间大小：
SELEct tablespace_@R_419_6889@,sum(bytes) / 1024 / 1024 as MB　from dba_data_files group by tablespace_@R_419_6889@;

--2、查看所有表空间对应的数据文件：
SELEct tablespace_@R_419_6889@,file_@R_419_6889@ from dba_data_files;

--3、修改数据文件大小：
alter database DATAFILE ‘H:\OracLE\PRODUCT\10.1.0\ORADATA\OracLE\USERS01.DBF‘ RESIZE 10240M;

SELEct file_@R_419_6889@,BYTES/1024/1024 MB from dba_data_files;