Getting Started With Oracle

Overview

Oracle is one the most popular Relational Database Management System (RDBMS).  Some other famous RDBMS includes Microsoft SQL Server, Sybase, MySQL, PostgreSQL, etc.  Essentially, all the aforementioned RDBMS employs Structural Query Language (SQL) as their query interface.  Users usually issue their queries by SQL through a "client".  Different RDBMS offer different forms of clients.  For example, MS SQL Server offers a GUI interface for user to type in their SQL language, and their queries would be executed after pressing the "Execute" button on the client.  Oracle provides both GUI client and command-line client.  In this lesson, we will study the command-line client, SQL*Plus.  In addition,  Oracle extends the standard SQL  (e.g. select * from table) with its application-specific commands (e.g. checking how many table you have been created in your Oracle account) into a Oracle specific language called PL/SQL.  In this tutorial, you will interact with Oracle database, thru SQL*Plus, by issuing a number of PL/SQL queries.

Logging In to Oracle [FOR ECOM-ICOM LAB ONLY]

Microsoft Windows

Under Windows environment, the Oracle client is called SQL*Plus.
Steps:

1.    Click Start, and then click Run.

2.    Type sqlplus, and fill in the username, password, and database name

3.    After you log in to SQL*Plus, you see the following message:

Connected to:

Oracle9i Enterprise Edition Release 9.1.7.0.0 - Production

JServer Release 9.1.7.0.0 - Production

      and you should receive the prompt:

SQL>

Changing Your Password

In response to the SQL> prompt, type

     alter user <yourName> identified by <newPassword>;

where <yourName> is again your login name, and <newPassword> is the password you would like to use in the future. This command, like all other SQL commands, should be terminated with a semicolon.

Creating Tables

In SQL*Plus we can execute any SQL command. One simple type of command creates a table (relation). The form is

     CREATE TABLE <tableName> (

         <list of attributes and their types>

     );

You may enter text on one line or on several lines. If your command runs over several lines, you will be prompted with line numbers until you type the semicolon that ends any command. (Warning: An empty line terminates the command but does not execute it; see editing commands in the buffer.) An example table-creation command is:

          CREATE TABLE test (

         i int,

         s char(10)

     );

Note that SQL is case insensitive, so CREATE TABLE TEST and create table test are the same. This command creates a table named test with two attributes. The first attribute, named i, is an integer, and the second, named s, is a character string of length (up to) 10.

Exercise 1:

Create a relation Student that suitable for the following instance:
 

Note: No need to insert the data yet!

Inserting Tuples

Having created a table, we can insert tuples into it. The simplest way to insert is with the INSERT command:

     INSERT INTO <tableName>

         VALUES( <list of values for attributes, in order> );

For instance, we can insert the tuple (10, 'hi world') into relation test by

            INSERT INTO test VALUES(10, 'hi world');

Exercise 2:

Insert the records as stated into Exercise 1 into the student table.

Trick: Try to insert a record into test with the following SQL:

         INSERT INTO test VALUES(11, 'ha 'world');

Updating Tuples

Tuples can be updated by the UPDATE command:

          UPDATE <tableName>

         SET <Attribute>=<Expression/Value>

     WHERE <Predicate>;

For example, we can update the tuple (10, 'hi world') in relation test by

     UPDATE test SET s='bye world' WHERE i=10;

Exercise 3:

Update the record of 'Eric Lo' in relation Student such that his salary change to 1234

Deleting Tuples

Having insert / update a tuple, we can delete it as well. The simplest way to delete is with the DELETE command:

       DELETE FROM <tableName> [WHERE <condition>];

<condition> is an optional statement and is used to identify a single record when necessary.

For example, you can delete the record with i=10 in table test with the the following SQL:

     DELETE FROM test WHERE i=10;

Exercise 4:

Delete the record of 'Eric Lo' in relation Student.

Trick: Does that record really deleted successfully?  Let's check it out by using SELECT command (we will cover it in next section).

Retrieving Tuples

We can see the tuples in a relation with the command:

      SELECT <attributes-separated-by-comma>/<wildcard>

      FROM <tableName>;

For instance, after the above CREATE, INSERT, DELETE and UPDATE statements, the command

     SELECT * FROM test;

produces the result

              I S

     ---------- ----------

             11 ha 'world

Exercise 5:

Select ALL records from relation Student.

Question: Do data values also case insensitive? i.e., can a student with name "Hammer" be retrieved by the following SQL or not?

     SeLecT name from StudenT where name ='hammer';

Let's check it out by yourself!

Trick: Does the record of  'Eric Lo' exist when you do exercise 5?  If yes, congratulation! You "seems" that you have deleted that tuple successfully...  Now, please open a new SQL*Plus, and redo exercise 5 to see if the record 'Eric Lo' still be there?  What happen?

Commit and Rollback

An automatic commit occurs under the following circumstance:

• DDL statement is issued
• Normal exit from SQL*Plus, without explicitly issuing COMMIT or ROLLBACK

An automatic rollback occurs under an abnormal termination of SQL*Plus or a system failure.

It provides a good back-door for you to revert the changes you have done on the data.  Therefore, unless you have issued COMMIT, the changed data would not be visible to any other session except your own. Conversely, you can rollback all the changes by issuing the ROLLBACK command.

Exercise 6:

Issue the COMMIT command in the SQL*Plus that you have done insert/delete/update before, and see if the effects is now visible by the new SQL*Plus?

Dropping Tables

To remove a table from your database, execute

     DROP TABLE <tableName>;

We suggest you execute

     DROP TABLE test;

Caution: Table dropping is a DML statement, which is an action that you cannot rollback.  Since dropping a table will also delete all data in that table, issue the DROP TABLE command with cares.

Getting Information About Your Database

The system keeps information about your own database in certain system tables. The most important for now is USER_TABLES. You can recall the names of your tables by issuing the query:

     SELECT TABLE_NAME

     FROM USER_TABLES;

More information about your tables is available from USER_TABLES. To see all the attributes of USER_TABLES, try:

     SELECT *

     FROM USER_TABLES;

It is also possible to recall the attributes of a table once you know its name. Issue the command:

     DESCRIBE <tableName>;

to view the schema of  <tableName>;

Quitting SQL*Plus

To leave SQL*Plus, type

     quit;

in response to the SQL> prompt.

Executing SQL From a File

Instead of executing SQL commands typed at a terminal, it is often more convenient to type the SQL command(s) into a file and cause the file to be executed. There are two ways to do so.

The first is to provide your login name, password and the name of the file in the command line with which you open SQL*Plus. The form of the command is:

     SQL*Plus <yourName>/<yourPassword> @<fileName>

For instance, if user scott, whose password is tiger, wishes to execute the file foo.sql, then he would execute the SQL in foo.sql by:

     SQL*Plus scott/tiger @foo

Notice that this mode presents a risk that scott's password will be discovered, so it should be used carefully. Also note that since scott did not specify an extension for the file name "foo", SQL*Plus implicitly assumes the default extension ".sql". Therefore, it is a good idea to give every command file an extension, and specify the complete file name with the extension after the "@".

A second, safer way, is for sally to log in to SQL*Plus as usual. He then types, in response to the SQL> prompt:

     @foo.sql

and the file foo.sql's contents will be executed.

Editing Commands in the Buffer

If you end a command without a semicolon, but with an empty new line, the command goes into a buffer. You may execute the command in the buffer by either the command RUN or a single slash (/).

You may also edit the command in the buffer before you execute it. Here are some useful editing commands. They are shown in upper case but may be either upper or lower.

Recording Your Session

You can use the spool command within SQL*Plus to dump your terminal output.  At the SQL> prompt, you type:

    spool foo;

and a file called foo.lst will appear in your current directory and will hold everything typed, until you exit SQL*Plus or type:

    spool off;

Help and Other Hints

In response to the SQL> prompt, type help followed by a keyword. If you are lucky, the keyword will be one of those for which help exists, and you will get a (somewhat) helpful message, usually ending in an example or two. To see all the possible commands, for each of which help is available, type

    help commands;

The output from help, and in general, the results of many SQL commands, can be too long to display on a screen. You can use

    set pause on;

to activate the paging feature.  When this feature is activated, output will pause at the end of each screen until you hit the "return" key. To turn this feature off, use

    set pause off;

Data Types

Here is part of the data types that are supported by Oracle.
 

Joining Tables

As mentioned in the lectures, joining is an essential step to retrieve information across different tables.  In SQL, there is no operator dedicated for joining.  Therefore, in order to join on two tables, you have do a Cartesian product on two tables and then specifying the conditions.

For example, you have another two tables table1 and table2 which is created by the following SQL:

     CREATE TABLE table1 (
         i int,
         s char(20)
     );

     CREATE TABLE table2 (
         i int,
         s char(20)
     );

Now, type 'ed' and open a text file to insert the following tuples into  table1 and table2:

         INSERT INTO table1 VALUES(1, 'table1one');
         INSERT INTO table1 VALUES(2, 'table1two');
         INSERT INTO table1 VALUES(3, 'table1three');
         INSERT INTO table1 VALUES(4, 'table1four');
         INSERT INTO table2 VALUES(4, 'table2four');
         INSERT INTO table2 VALUES(5, 'table2five');
         INSERT INTO table2 VALUES(6, 'table2six')
/

Then, you have join the two tables with the following SQL:

          SELECT * FROM  table1 t1, table2 t2
    WHERE t1.i = t2.i;

Exercise 6: (A mini quiz)

1) Create another table call Streams with the following values:

2) Join the table Student and Streams to list the information the

• sid
• name
• job
• salary
• stream

   of students with salary > 6500

Functions

Oracle offers some numeric and string functions for users to display the result in a more desirable format.  For example, the SUBSTR(A, 1, 4) function returns the first four characters for every data value.  Therefore, the SQL:

        SELECT SUBSTR(Stream_Name, 1,3) as XXX FROM Streams;

will the result like this:

                  XXX

     ----------

            Eco

            Ico  

The following table gives you an overview of a subset of functions Oracle provided:

Aggregate Functions and Group-By Clause

We would demonstrate the aggregate functions and group-by clause by a number of SQL queries.

1.  Find the average salary of students in Ecom Stream

     SELECT AVG(Salary) FROM Student WHERE Stream = 'I';

2.  Find the average salary of students in each Stream

     SELECT Stream, AVG(Salary) FROM Student GROUP BY Stream;

3.  Find the total number of students

     SELECT COUNT(*) FROM Student;

4.  Find the total number of student in each Stream

     SELECT COUNT(*), StrEAM FROM Student GROUP BY Stream;

5.  Find the total number of student in each Stream that have more than 2 students

     SELECT COUNT(*) FROM Student GROUP BY Stream HAVING COUNT(*) > 2;

Creating Tables with Keys

To create a table that declares attribute a to be a primary key:

     CREATE TABLE <tableName> (..., a <type> PRIMARY KEY, b, ...);

To create a table that declares the set of attributes (a,b,c) to be a primary key:

     CREATE TABLE <tableName> (<attrs and their types>, PRIMARY KEY (a,b,c));

Creating Index

In fact, a unique key is created automatically when you define a PRIMARY KEY in table definition.

To create an index on or more columns explicitly, you can:

     CREATE INDEX <index> on <table> (column 1, ..., column n);