oracle创建dblink问题

1 prepaid =
2 　　(DESCRIPTION =
3 　　(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.100.4)(PORT = 1521))
4 　　(CONNECT_DATA =
5 　　(SERVER = DEDICATED)
6 　　(SID = prepaid)
7 　　)
8 　　)

1 prepaid =
2 　　(DESCRIPTION =
3 　　(ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
4 　　(CONNECT_DATA =
5 　　(SERVER = DEDICATED)
6 　　(SID = prepaid)
7 　　)
8 　　)

1 create public database link linkname connect to s_user identified by s_pwd using ‘prepaid‘;

SQL> select * from scott.emp@mylink;
select * from scott.emp@mylink
                        *
第 1 行出现错误:
ORA-12154: TNS: 无法解析指定的连接标识符

create public database link dblinkname connect to username identified by password
　　 using ‘(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = database_ip)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME =servicename)
)
)‘;