去掉123456两边的单引号试试，，，为什么又是单引号又是双引号？

还是不行

11gR2 Database Link: ORA-01017 & ORA-02063 When Using Lower Case Identifiers (Doc ID 1677916.1)

创建dblink有问题吧

system也不行

SOLUTION
Either:

1. Create the link with no quotes around the username/password so that the credentials are interpreted in uppercase.

SQL> create database link TARGET_DB CONNECT TO IDENTIFIED BY USING ‘TARGET_DB’;

Alternatively:

2. If it is your convention or if creating the dblinks are scripted, you could create the link using quoted identifiers AND in uppercase:

SQL> create database link OTARGET_DB CONNECT TO “” IDENTIFIED BY “” USING ‘TARGET_DB’;

It is not possible to use quoted userid/password identifiers in the creation of a link. You will not be able to successfully select across that link.

system不要引号

解决了，谢谢大佬