为什么我必须双重引用模式名称和表名才能从Oracle表中查询？

Question

我是Oracle的新手,我遇到了以下问题.为什么我必须双重引用模式名称和表名才能从表中查询？有没有改变它的设置？

谢谢.

SQL> conn sys/ogrish@orcl as sysdba
Connected.
SQL> show user
USER is "SYS"
SQL> select * from v$version;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for 64-bit Windows: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production

SQL> select * from m.album;
select * from m.album
                *
ERROR at line 1:
ORA-00942: table or view does not exist


SQL> select * from M.Album where rownum < 2;
select * from M.Album where rownum < 2;
              *
ERROR at line 1:
ORA-00942: table or view does not exist

SQL> select * from "M"."Album" where rownum < 2;

   AlbumId Title
---------- ----------------------------------------------------------------------
         1 For Those About To Rock We Salute You

SQL> conn m/m@orcl
Connected.
SQL> select table_name from user_tables;

TABLE_NAME
------------------------------
Album
Artist
Customer
Employee
Genre
Invoice
InvoiceLine
MediaType
Playlist
PlaylistTrack
sysdiagrams

TABLE_NAME
------------------------------
Track

12 rows selected.

SQL> select * from album where rownum < 2;
select * from album where rownum < 2;
              *
ERROR at line 1:
ORA-00942: table or view does not exist


SQL> select * from Album where rownum < 2;
select * from Album where rownum < 2
              *
ERROR at line 1:
ORA-00942: table or view does not exist


SQL> select * from m.album where rownum < 2;
select * from m.album where rownum < 2
                *
ERROR at line 1:
ORA-00942: table or view does not exist


SQL> select * from M.Album where rownum < 2;
select * from M.Album where rownum < 2
                *
ERROR at line 1:
ORA-00942: table or view does not exist


SQL> select * from "M"."Album" where rownum < 2;

   AlbumId Title
---------- ----------------------------------------------------------------------
         1 For Those About To Rock We Salute You

SQL> select * from "Album" where rownum < 2;

   AlbumId Title
---------- ----------------------------------------------------------------------
         1 For Those About To Rock We Salute You

SQL>

Answer 1

您不必在模式名称上添加双引号,但是您必须在表名称上执行此操作,因为您使用引号创建它(使其区分大小写):

select * from M."Album"

也应该工作.否则M.Album默认转换为M.ALBUM - 并且表ALBUM不存在.