Select Clauses in SQL Part1

SQL> create table student_master(Name varchar(20),Reg_no number(5),dept varchar(20),year number(4));
Table created.
SQL> insert into student_master values('&name',&Reg_no,'&dept', &year);
Enter value for name: Navin
Enter value for reg_no: 001
Enter value for dept: BCA
Enter value for year: 1991
old   1: insert into student_master values('&name',&Reg_no,'&dept', &year)
new   1: insert into student_master values('Navin',001,'BCA', 1991)
1 row created.
SQL> /
Enter value for name: Neenu
Enter value for reg_no: 002
Enter value for dept: BCA
Enter value for year: 1989
old   1: insert into student_master values('&name',&Reg_no,'&dept', &year)
new   1: insert into student_master values('Neenu',002,'BCA', 1989)
1 row created.
SQL> /
Enter value for name: XXX
Enter value for reg_no: 003
Enter value for dept: BCA
Enter value for year: 1990
old   1: insert into student_master values('&name',&Reg_no,'&dept', &year)
new   1: insert into student_master values('XXX',003,'BCA', 1990)
1 row created.
SQL> SELECT * FROM STUDENT_MASTER;
NAME             REG_NO DEPT                  YEAR
---------------- ---------- ---------------- ----------
Navin            1 BCA                        1991
Neenu            2 BCA                        1989
XXX              3 BCA                        1990
SQL> SELECT NAME FROM STUDENT_MASTER;
NAME
--------------------
Navin
Neenu
XXX
SQL> SELECT DISTINCT (REG_NO),NAME,DEPT,YEAR FROM STUDENT_MASTER;
REG_NO NAME            DEPT              YEAR
----- ---------------- ----------------- ----------
    1 Navin            BCA               1991
    2 Neenu            BCA               1989
    3 XXX              BCA               1990
SQL> SELECT DISTINCT * FROM STUDENT_MASTER ORDER BY REG_NO DESC;
NAME           REG_NO     DEPT     YEAR
-------------- ---------- -------- ----------
XXX                     3 BCA      1990
Neenu                   2 BCA      1989
Navin                   1 BCA      1991
SQL> SELECT * FROM STUDENT_MASTER  WHERE DEPT = 'BCA';
NAME           REG_NO     DEPT     YEAR

-------------- ---------- -------- ----------

XXX                     3 BCA      1990

Neenu                   2 BCA      1989

Navin                   1 BCA      1991