Before we access oracle database, we must start
oracle database. Starting up oracle database means starting oracle instance and
associating oracle instance with an oracle database so that oracle instance can
access the database.
The process is very length and complicated.
Several steps are involved in it. But fortunately we do not have to know all
that happens when a database starts. We just need to select an option or two to
startup database.
Generally you do not have to startup database in
case of Oracle Server running on Windows NT/Windows 2000 as oracle server
automatically starts in this case. However, if you ever have to start oracle
database on Windows NT/Windows 2000, follow the steps given below:
1. Start services program using Administrative Tools -> Service in
Windows/2000 or Control Panel -> Service on Windows NT.
2. If service OracleServiceOracle8i has not yet started,
click on it with right button and select start option from popup menu.
The exact name of the
service depends on the name you have given to oracle instance at the time of
installing it.
Note: Starting
and shutting down the database is the job of Database Administrator. As this
books assumes that you are an application developer, it doesn’t get into those
details.
Starting up database in Personal Oracle
Unlike Oracle Server in Personal Oracle, Oracle
Instance doesn’t start on its own. The Oracle Instance must be explicitly
started. The following are the steps to start oracle on Personal Oracle:
1.
Select start database
option in Personal Oracle8i for windows menu.
2.
When a dialog box is displayed
wait until the message Oracle Instance Started appears.
3.
Click on Close button to
close the dialog box.
Starting SQL*PLUS
Sql*plus is a tool that comes along with Oracle.
It is used to issue SQL and SQL*PLUS commands. It provides command line
interface through which we can enter SQL and SQL*PLUS command.
To start SQL*PLUS, take the steps given below:
1.
Select start->programs->Oracle
- Oracle8i.
Oracle8i is the name of the instance. It
may be different on your system.
2.
Then select Application
Development -> SQL Plus.
3.
When Log On dialog box
is displayed, enter username, password and Host string.
Use tab key to move from one field to another.
For more information about each of these fields, see next section.
4.
Click on OK.
5.
If the information supplied is
valid then you enter into Oracle and SQL*PLUS will display SQL> prompt.
Username, Password and Host String
Oracle is a multi-user database. Whoever is
access the database must log on to database.
To log on we have to supply username and password. When the given username and password are
recognized by Oracle, it will allow us to access data. A user can access only the data that belongs
to his/her and not the data of others.
However, it is possible for a user to grant privileges to others so that
other can access his/her data.
Creation of users and management of overall
security is the responsibility of Database Administrator (DBA). DBA is the person who makes sure that
database is functioning smoothly. He is responsible for operations such as
taking backup of the database, recovering the database in the event of failure,
fine tuning database to get best performance. So, if you want to have a new
account under your name, please consult administrator of your database.
Username & Password
Every user who wants to access oracle database
must have an account in the database. These accounts are created by DBA. Each
account is associated with username and password.
Oracle comes with a set of predefined accounts.
The following are the usernames and passwords of these accounts.
Username Password
system manager
sys change_on_install
Scott tiger
Demo demo
Note: when you
enter into oracle using either system or sys then you become DBA.
That means you get special privileges to perform major operations such as
creating users etc.
Host String
Host string is a name that is used to access
oracle server that is running on a different machine from client. This is
required only when you are trying to access oracle server that is not on the
current machine. That means, you never need to use host string for Personal
Oracle as client and oracle always run on the same machine in Personal Oracle.
Host string is required when you are trying to
connect to Oracle Server running on remote machine. Host string is actually called as net
service name. Net service name is a name that is stored in TNSNAMES.ORA
file on the client to provide the following information.
Host
|
Name of the machine or IP address of the
machine on which oracle server is running.
|
Instance name
|
Name of the Oracle Instance running on the
remote machine.
|
Port Number
|
Port number of the listener, a program that
takes requests from clients. Port
number is an integer that uniquely identifies the program on the server.
|
How to enter SQL statements?
SQL*PLUS allow to types of command to entered at
the prompt - SQL and SQL*PLUS.
SQL commands include commands of ANSI/ISO SQL
and extra commands added to ANSI SQL by oracle.
The following are the rules to be followed while
entering SQL commands.
1.
An SQL statement may be entered
in multiple lines.
2.
It is not possible to break a
word across lines.
3.
SQL statement must be
terminated by semicolon (;).
The following is an example of SQL command. What this command does is not important at
this moment.
SQL> select ccode,name
2 from courses
3 where fee > 5000;
In the above command, we entered the command in
three lines. When you enter semicolon and press enter key then SQL*PLUS will
take it as the end of the command. Also note that you have to press enter key
at the end of each line.
Note: Both SQL
and SQL*PLUS commands are NOT case sensitive.
How to enter SQL*PLUS statements?
SQL*Plus statements are available only in
SQL*PLUS. They are not part of standard SQL. SQL*Plus commands are mainly used
for two purposes – editing SQL commands and formatting result of query.
The following rules are to be followed while
entering these commands.
1.
The entire command must be
entered on a single line.
2.
No need to terminate command
with semicolon (;).
3.
Commands can be abbreviated.
However, the amount of abbreviation is not fixed. Some commands are abbreviated to one letter
some are abbreviated to 2 and so on.
The following example show how to use CLEAR
SCREEN command of SQL*PLUS.
SQL>clear screen
Or it can be abbreviated to
SQL>cl scr
Common Errors
The following are the common errors that you get
while you are trying to log on to Oracle.
Ora-01017: invalid username/password; login
denied
The reason for this error is that you have entered
a username or password that is not valid. Check whether username you are
entering is really existing and password is correctly typed. Sql*plus gives you three chances to type
username and password correctly. If you
cannot log on successfully in three chances then Sql*plus will exit.
However, you can restart Sql*plus again.
ORA-01034: ORACLE not available
The reason for this message is that Oracle
Instance is not up and running. You have to first make sure you have started
Oracle Instance. Actually there are a
few other problems that occurs when Oracle Instance has not started
successfully. If this is case in Oracle Server, notify administrator. If this
is the case with Personal Oracle, make sure you start database as mentioned in
“starting up database” section.
Summary
In this chapter, we have seen what is Oracle and
what is the difference between Oracle Server and Personal Oracle. We have seen
how to connect to Oracle through SQL*Plus.
In the next chapter, we start creating tables
and understanding elementary statements in SQL.
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