问题：Oracle主服务和监听器服务已经启动，使用SQL Plus能够正常连接，使用PL SQL Developer连接报次错误：ORA-12514: TNS: 监听程序当前无法识别连接描述符中请求的服务。如图：
解决：
打开H:\Oracle\product\11.2.0\dbhome_1\NETWORK\ADMIN（不同机器目录可能不同）目录下的listener.ora文件，发现此文件内容如下：
- #listener.ora Network Configuration File:
- H:\Oracle\product\11.2.0\dbhome_1\network\admin\listener.ora
- #Generated by Oracle configuration tools.
- SID_LIST_LISTENER=
- (SID_LIST =
- (SID_DESC =
- (SID_NAME = CLRExtProc)
- (ORACLE_HOME =H:\Oracle\product\11.2.0\dbhome_1)
- (PROGRAM = extproc)
- (ENVS ="EXTPROC_DLLS=ONLY:H:\Oracle\product\11.2.0\dbhome_1\bin\oraclr11.dll")
- )
- )
- LISTENER=
- (DESCRIPTION_LIST =
- (DESCRIPTION =
- (ADDRESS = (PROTOCOL = IPC)(KEY =EXTPROC1521))
- (ADDRESS = (PROTOCOL = TCP)(HOST =localhost)(PORT = 1521))
- )
- )
- ADR_BASE_LISTENER= H:\Oracle
修改成如下内容（注意红色部分的内容）：
#listener.ora Network Configuration File:
H:\Oracle\product\11.2.0\dbhome_1\network\admin\listener.ora
#Generated by Oracle configuration tools.
SID_LIST_LISTENER=
(SID_LIST =
(SID_DESC =
(GLOBAL_DBNAME = ORCL)
(ORACLE_HOME =H:\Oracle\product\11.2.0\dbhome_1)
(SID_NAME = ORCL)
)
(SID_DESC =
(SID_NAME = CLRExtProc)
(ORACLE_HOME = H:\Oracle\product\11.2.0\dbhome_1)
(PROGRAM = extproc)
(ENVS ="EXTPROC_DLLS=ONLY:H:\Oracle\product\11.2.0\dbhome_1\bin\oraclr11.dll")
)
)
LISTENER=
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = IPC)(KEY =EXTPROC1521))
(ADDRESS = (PROTOCOL = TCP)(HOST =localhost)(PORT = 1521))
)
)
ADR_BASE_LISTENER= H:\Oracle
说明：每台电脑的Oracle安装目录和实例名不尽相同，修改此文件的ORACLE_HOME（本机Oracle安装目录）和SID_NAME应该按照你自己的设置。
SID查看请参照此图：