在已建好的table上添加primary key1.建立索引create  index test_idx on test(id);2.添加約束alter table testadd constraint test_pk primary key (id)using index test_idx; 在SQLPLUS中登陸時出現以下錯誤ERROR:ORA-12638: Credential retrieval failed解決方法:修改sqlnet.ora如果SQLNET.AUTHENTICATION_SERVICES=  (NTS)一行沒有被注釋,則注釋掉#SQLNET.AUTHENTICATION_SERVICES=  (NTS)反之取消注釋 ALTER SYSTEM SET EVENTS=@#10231 trace name context forever,level 10@# ; 内部事件，设置在全表扫描时跳过损坏的数据块. 查看tablespace的空間使用情況select a.tablespace_name, trunc(sum(b.bytes/1024/1024),2) "FREE(M)", trunc(sum(a.bytes/1024/1024)-sum(b.bytes/1024/1024),2) "USED(M)", trunc(sum(a.bytes/1024/1024),2) "ALL(M)", trunc(sum(b.bytes/1024/1024)/sum(a.bytes/1024/1024),2)*100||@#%@# "Free(%)"from  dba_data_files ajoin  dba_free_space b  on(a.file_id=b.file_id)group by a.tablespace_name;如何指定tnsname.ora的位置設置環境變量TNS_ADMIN 獲取當前SCN(9i以後)select dbms_flashback.get_system_change_number from dual;