[b]case 1.[/b]

select * from emp
is same as
select * from EMP

[b]case 2.[/b]
but when u use table_name in where clause it should CAPS by defualt( becuase oracle stores it as such).

SQL> select * from cat where table_name='emp';

no rows selected

SQL> select * from cat where table_name='EMP';

TABLE_NAME                     TABLE_TYPE
------------------------------ -----------
EMP                            TABLE

[b]case 3:[/b]
under considerations (which is not recomended) u can create a table with small caps ie..emp.

SQL> create table "emp1" as select * from emp;

Table created.
SQL> select * from cat where table_name='emp1';

TABLE_NAME                     TABLE_TYPE
------------------------------ -----------
emp1                           TABLE

SQL> select * from cat where table_name='EMP1';

TABLE_NAME                     TABLE_TYPE
------------------------------ -----------
EMP1                           TABLE