Oracle DB服务已打开，但Oracle SQL Developer软件中仍出现数据库未打开错误

我使用的是Oracle DB版本为19c和SQL Developer软件版本为21

我已尝试连接Oracle SQL Developer，但出现以下错误：

An error was encountered performing the requested operation:

ORA-01109: database not open
01109. 00000 -  "database not open"
*Cause:    A command was attempted that requires the database to be open.
*Action:   Open the database and try the command again
Vendor code 1109

我认为Oracle服务已关闭，因此通过以下命令在SQL Plus软件中签入它

Enter user-name: system
Enter password:
Last Successful login time: Fri Jan 14 2022 12:05:59 +05:30

Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0

SQL> ALTER DATABASE OPEN;
ALTER DATABASE OPEN
*
ERROR at line 1:
ORA-01531: a database already open by the instance


SQL> select status from v$instance;

STATUS
------------
OPEN

Oracle DB服务已打开，但在Oracle SQL Developer software中仍出现‘数据库未打开’错误。

请参阅所附屏幕截图。

请建议问题是什么，我们如何解决它？非常感谢。

pdb

您正在处理推荐答案。您的根数据库已启动，但您没有启动PDB。

SQL> conn / as sysdba
Connected.
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area  713028296 bytes
Fixed Size                  9138888 bytes
Variable Size             545259520 bytes
Database Buffers          150994944 bytes
Redo Buffers                7634944 bytes
Database mounted.
Database opened.
SQL> conn system/pwd@pdb01
ERROR:
ORA-01109: database not open


Warning: You are no longer connected to ORACLE.
SQL> conn / as sysdba
Connected.
SQL> alter pluggable database all open;

Pluggable database altered.

SQL> conn system/pwd@pdb01
Connected.