症：PL/SQL无法找到数据库

提要：Win7（64Bit）旗舰系统下的 Oracle，PL/SQL只有32位

解决：

1. 下载并解压 Oracle Technology Network  

　　下载地址： http://www.oracle.com/technetwork/topics/winsoft-085727.html

　　解压到地址（非强制）：..\TOOLS_APP\instantclient_12_1

2.在上面建立的目录下新建目录：..\instantclient_12_1\network\admin

　　并新建文件：tnsnames.ora

　　内容如下：

# tnsnames.ora Network Configuration File: E:\oracle\product\11.2.0\dbhome_1\network\admin\tnsnames.ora
# Generated by Oracle configuration tools.

LISTENER_ORCL =
(ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))

ORACLR_CONNECTION_DATA =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
)
(CONNECT_DATA =
(SID = CLRExtProc)
(PRESENTATION = RO)
)
)

ORCL =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = orcl)
)
)

3.非登陆状态下进入PL_SQL，

　　打开Tools -> Preferences -> Oracle -> Connection：
　　设置：Oracle_Home： E:\oracle\TOOLS_APP\instantclient_12_1
　　设置：OCI Library： E:\oracle\TOOLS_APP\instantclient_12_1\oci.dll

4.重启PL_SQL