我也有同样的问题。对我来说，就是写作

sqlplus myusername/mypassword@localhost

这样做使它连接到默认的服务名，我猜。

我有一个案例，我使用DBMS，我必须完成一个数据库连接表单。

我把SID放入数据库字段，在下拉框中，在字段旁边，我有“服务名称”值而不是“SID”值。 (通常我不使用Oracle数据库，所以我没有意识到差异)

这就是我得到错误消息的原因。

当应用程序为每个数据库交互建立新连接或连接未正确关闭时，可能会发生此错误。监视和确认这一点的免费工具之一是Oracle Sql developer(尽管这不是您可以用来监视DB会话的唯一工具)。

您可以从oracle网站Sql Developer下载该工具

下面是如何监控你的会话的截图。(如果您在看到ORA-12514错误时看到应用程序用户堆积了许多会话，那么这很好地表明您可能有连接池问题)。

这里有很多答案，但这里有一个工作示例的代码，你可以立即复制、粘贴和测试:

对我来说，在指定正确的SERVICE_NAME后，错误12514得到了解决。 您可以在服务器上的文件tnsnames中找到它。ora自带3个预定义的服务名称(其中一个是“XE”)。

I installed the Oracle Express database OracleXE112 which already comes with some preinstalled demo tables. When you start the installer you are asked for a password. I entered "xxx" as password. (not used in production) My server runs on the machine 192.168.1.158 On the server you must explicitely allow access for the process TNSLSNR.exe in the Windows Firewall. This process listens on port 1521. OPTION A: For C# (.NET2 or .NET4) you can download ODAC11, from which you have to add Oracle.DataAccess.dll to your project. Additionally this DLL depends on: OraOps11w.dll, oci.dll, oraociei11.dll (130MB!), msvcr80.dll. These DLLs must be in the same directory as the EXE or you must specify the DLL path in: HKEY_LOCAL_MACHINE\SOFTWARE\Oracle\ODP.NET\4.112.4.0\DllPath. On 64 bit machines write additionally to HKLM\SOFTWARE\Wow6432Node\Oracle\... OPTION B: If you have downloaded ODAC12 you need Oracle.DataAccess.dll, OraOps12w.dll, oci.dll, oraociei12.dll (160MB!), oraons.dll, msvcr100.dll. The Registry path is HKEY_LOCAL_MACHINE\SOFTWARE\Oracle\ODP.NET\4.121.2.0\DllPath OPTION C: If you don't want huge DLL's of more than 100 MB you should download ODP.NET_Managed12.x.x.x.xxxxx.zip in which you find Oracle.ManagedDataAccess.dll which is only 4 MB and is a pure managed DLL which works in 32 bit and 64 bit processes as well and depends on no other DLL and does not require any registry entries. The following C# code works for me without any configuration on the server side (just the default installation):

using Oracle.DataAccess.Client;
or
using Oracle.ManagedDataAccess.Client;

....

string oradb = "Data Source=(DESCRIPTION="
    + "(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.1.158)(PORT=1521)))"
    + "(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=XE)));"
    + "User Id=SYSTEM;Password=xxx;";

using (OracleConnection conn = new OracleConnection(oradb)) 
{
    conn.Open();
    using (OracleCommand cmd = new OracleCommand())
    {
        cmd.Connection  = conn;
        cmd.CommandText = "select TABLESPACE_NAME from DBA_DATA_FILES";

        using (OracleDataReader dr = cmd.ExecuteReader())
        {
            while (dr.Read())
            {
                listBox.Items.Add(dr["TABLESPACE_NAME"]);
            }
        }
    }
}

如果SERVICE_NAME=XE错误，则会得到错误12514。SERVICE_NAME是可选的。你也可以把它放在一边。

检查数据库是否启动。登录到服务器，将ORACLE_SID环境变量设置为您的数据库SID，并作为本地连接运行SQL*Plus。

我知道这是一个老问题，但仍然没有答案。我花了一天的时间研究，但我找到了最简单的解决方案，至少在我的情况下(Windows 2008 R2上的Oracle 11.2)，我想分享。

如果直接查看该错误，则表明侦听器不识别服务名称。但是它把服务名保存在哪里呢?在% ORACLE_HOME % \ \ ADMIN \ listener.ora网络

“SID_LIST”就是一个sid和服务名的列表，它们以一种可以复制或查找的格式配对。

我添加了问题服务名称，然后在Windows“服务”控制面板中，我对Oracle侦听器服务进行了“重新启动”。现在一切都好了。

例如，你的听众。Ora文件最初可能是这样的:

# listener.ora Network Configuration File: C:\app\oracle_user\product\12.1.0\dbhome_1\network\admin\listener.ora
# Generated by Oracle configuration tools.

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
      (SID_NAME = CLRExtProc)
      (ORACLE_HOME = C:\app\oracle_user\product\12.1.0\dbhome_1)
      (PROGRAM = extproc)
      (ENVS = "EXTPROC_DLLS=ONLY:C:\app\oracle_user\product\12.1.0\dbhome_1\bin\oraclr12.dll")
    )
  )

LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
    )
  )

．.． 为了让它识别orcl的服务名称，你可以将它更改为:

# listener.ora Network Configuration File: C:\app\oracle_user\product\12.1.0\dbhome_1\network\admin\listener.ora
# Generated by Oracle configuration tools.

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
      (SID_NAME = CLRExtProc)
      (ORACLE_HOME = C:\app\oracle_user\product\12.1.0\dbhome_1)
      (PROGRAM = extproc)
      (ENVS = "EXTPROC_DLLS=ONLY:C:\app\oracle_user\product\12.1.0\dbhome_1\bin\oraclr12.dll")
    )
    (SID_DESC = 
        (GLOBAL_DBNAME = orcl)
        (ORACLE_HOME = C:\app\oracle_user\product\12.1.0\dbhome_1)
        (SID_NAME = orcl)
    )
  )

LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
    )
  )