切换pdb时报错：
SQL> alter session set container=pdb3;
ERROR:
ORA-44787: Service cannot be switched into.
SQL> !oerr ora 44787
44787, 0000, "Service cannot be switched into."
// *Document: Yes
// *Cause: The service did not exist in the new pluggable database or the service was not started in the pluggable database.
// *Action: Use a valid service name for the pluggable database or start the service in the pluggable database first.
检查服务名及注册情况：
----service
SQL> column con_id format 99
SQL> column pdb format a15
SQL> column network_name format a30
select con_id, pdb, network_name from cdb_services where pdb is not null and con_id > 2 order by pdb;SQL> SQL> SQL>
CON_ID PDB NETWORK_NAME
------ --------------- ------------------------------
3 PDB3 pdb3.localdomain
---lsnr
$ lsnrctl status
LSNRCTL for Linux: Version 12.2.0.1.0 - Production on 07-NOV-2022 03:30:37
Copyright (c) 1991, 2016, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=prodb)(PORT=1521)))
STATUS of the LISTENER
------------------------
Alias LISTENER
Version TNSLSNR for Linux: Version 12.2.0.1.0 - Production
Start Date 07-NOV-2022 03:27:35
Uptime 0 days 0 hr. 3 min. 1 sec
Trace Level off
Security ON: Local OS Authentication
SNMP OFF
Listener Parameter File /u01/app/oracle/product/19/network/admin/listener.ora
Listener Log File /u01/app/oracle/diag/tnslsnr/prodb/listener/alert/log.xml
Listening Endpoints Summary...
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=prodb)(PORT=1521)))
(DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))
Services Summary...
Service "CDB1" has 1 instance(s).
Instance "CDB1", status UNKNOWN, has 1 handler(s) for this service...
Service "CDB1.localdomain" has 1 instance(s).
Instance "CDB1", status READY, has 1 handler(s) for this service...
Service "CDB1XDB.localdomain" has 1 instance(s).
Instance "CDB1", status READY, has 1 handler(s) for this service...
Service "CDB2" has 1 instance(s).
Instance "CDB2", status UNKNOWN, has 1 handler(s) for this service...
Service "DB12" has 1 instance(s).
Instance "DB12", status UNKNOWN, has 1 handler(s) for this service...
Service "DB11" has 2 instance(s).
Instance "DB11", status UNKNOWN, has 1 handler(s) for this service...
Instance "DB11", status READY, has 1 handler(s) for this service...
Service "CDB3" has 1 instance(s).
Instance "CDB3", status UNKNOWN, has 1 handler(s) for this service...
The command completed successfully
未发现pdb3.localdomain注册到监听
解决办法：
SQL> alter pluggable database pdb3 close immediate;
SQL> alter pluggable database pdb3 open;
SQL> alter session set container=pdb3;
参考：
Connecting to PDB fails with ORA-44787 or ORA-600 [kpopappe: Service Is Null!] error (文档 ID 2630826.1)
