Hello Atish,
The basic aim behind defining the primary key in the table is to identify the record uniquely from ur table. The primary key is a set of one or more number of attributes which when taken collectively will identify the record uniquely from ur table. The syntax for defining a table is
create table <table name> (attribute1 datatype(size),attribute2 datatype(size),.............,primary key(atrributei));
create table students (rno number(3),name varchar2(20),.........................,primary key(rno));
This constraint of primary key imposes the constraints UNIQUE & NOT NULL on ur attribute(s).
Just try it.
If u have any problem u can still ask me / mail me at
sssupase@gmail.com See u.