修改t01用户的密码为test&test
SQL> alter user t01 idendified by "test&test";
Enter value for test: 
无法正常修改

下面介绍两种方法
1.
SQL> show define
define "&" (hex 26)
SQL> set define off
SQL> show define
define OFF
SQL> alter user t01 identified by "test&test";
User altered.
SQL> conn t01/test&test;
Connected.

2.
SQL> show escape
escape OFF
SQL> set escape on
SQL> show escape
escape "\" (hex 5c)
SQL> alter user t01 identified by "test\&test";
User altered
SQL> conn t01/test\&test
Connected.

上面连个参数会话断开后失效。