SQL Joins through Visual illustration

http://www.codeproject.com/Articles/33052/Visual-Representation-of-SQL-Joins

how to create user schema in oracle db

Connect or login as sysdba account

sqlplus sys/password AS SYSDBA

To create user schema

create user username Identified by password DEFAULT TABLESPACE users TEMPORARY TABLESPACE temp QUOTA UNLIMITED ON users;

You have to give grants to according to your requirement

GRANT CONNECT, CREATE TABLE TO username;

Reference :http://www.oracle-base.com/articles/misc/SchemaOwnersAndApplicationUsers.php