Question

How to create a small and simple database using Oracle 11 g and SQL Developer ?
I am seeing too many errors and I cannot find any way to make a simple database.
For example

create database company; 

Caused the following error:

Error starting at line 1 in command:
create database company
Error at Command Line:1 Column:0
Error report:
SQL Error: ORA-01501: CREATE DATABASE failed
ORA-01100: database already mounted
01501. 00000 -  "CREATE DATABASE failed"
*Cause:    An error occurred during create database
*Action:   See accompanying errors.

EDIT-
This is completely different from MySQL and MS-SQL that I am familiar with.
Not as intuitive as I was expecting.

Answer 1

First off, what Oracle calls a “database” is generally different than what most other database products call a “database”. A “database” in MySQL or SQL Server is much closer to what Oracle calls a “schema” which is the set of objects owned by a particular user. In Oracle, you would generally only have one database per server (a large server might have a handful of databases on it) where each database has many different schemas. If you are using the express edition of Oracle, you are only allowed to have 1 database per server. If you are connected to Oracle via SQL Developer, that indicates that you already have the Oracle database created.

Assuming that you really want to create a schema, not a database (using Oracle terminology), you would create the user

CREATE USER company
  IDENTIFIED BY <<password>>
  DEFAULT TABLESPACE <<tablespace to use for objects by default>>
  TEMPORARY TABLESPACE <<temporary tablespace to use>>

You would then assign the user whatever privileges you wanted

GRANT CREATE SESSION TO company;
GRANT CREATE TABLE TO company;
GRANT CREATE VIEW TO company;
...

Once that is done, you can connect to the (existing) database as COMPANY and create objects in the COMPANY schema.