SQL> CREATE USER testuser1 IDENTIFIED BY "Cat"

2 DEFAULT TABLESPACE users

3 TEMPORARY TABLESPACE temp;

User created.

　　SQL> CREATE USER testuser2 IDENTIFIED BY "H@t"

　　2 DEFAULT TABLESPACE users

　　3 TEMPORARY TABLESPACE temp;

　　User created.

　　SQL> GRANT create session TO testuser1, testuser2;

　　Grant succeeded.

　　SQL> connect testuser1/cat

　　Connected.

　　SQL> connect testuser2/h@t

　　ERROR:

　　ORA-12154: TNS:could not resolve the connect identifier specified

　　Warning: You are no longer connected to ORACLE.

　　SQL> connect testuser2/"h@t"

　　Connected.

　　SQL>

　　The workaround is to enclose the password in quotes, as shown in the listing.