连接Oracle报错：listener does not currently know of service requested in connect descriptor

解决办法：修改环境变量的配置

原来环境变量TNS_ADMIN如下：即配置的是客户端instantclient的

 现在该为Oracle服务器的，

D:appmiracleproduct11.2.0dbhome_2NETWORKADMIN

 再来模拟一下问题：

条件：

1、环境变量中TNS_ADMIN为客户端instantclient的，即D:installinstantclientinstantclient_19_12NETWORKADMIN

2、D:installinstantclientinstantclient_19_12NETWORKADMIN目录下的tnsnames.ora文件内容如下：

ORCL1 =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = orcl)
    )
  )

当我们修改ORCL1为ORCL时，

ORCL =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = orcl)
    )
  )

此时，用PLSQL访问Oracle数据库，

 此时会报错：

 解决办法：将环境变量的TNS_ADMIN的变量值改为Oracle服务的，即D:appmiracleproduct11.2.0dbhome_2NETWORKADMIN，

 再重启如下四个Oracle服务：

 再次用PLSQL访问Oracle数据库，此时就可以登录了。