The Role of Taxonomy and Ontology in Semantic Layers - Heather Hedden.pdf
Introduction to database
1.
2. In our programs we use variables to store
information.
But when our program terminates all the
variables declared in it disappear.
Why this happens????
3. What if we need some information to be
stored even after the termination of
program. (We are here in this session for
this need).
How can we fulfill this need?
Any suggestion……..
4. The most simple solution is store the
information in the disk.
Now the question is how we can store in
disk.
Create a file and store there.(simple
enough)
Is it a good solution or the best solution ?
5.
6. Suppose we want to implement the log in
section.(feature 1)
We use a file and store the user_id and
password in the following manner
7. When 1105120 wants to log in we have to
check all the previous record.
Also we have to check whether multiple
users are accessing the file.
Any more problem………….
8. So we need to care about a lot of facts
beside storing, updating the file.
But we are lazy people. We always want to
minimize our task.(At least me!)
Thank GOD there are some applications or
Systems which handle the facts about
which we were worried
9. And
they are called DataBase
Management System(DBMS).
• Oracle
• IBM DB2
• Microsoft SQL Server
• Microsoft Access
• PostgreSQL
• MySQL
• SQLite
10. But not all our problems have been solved.
Why???
Because now we have to learn how to
maintain Database using DBMS .
Here we will see how to manage database
using MySQL.
11. CREATE DATABASE [IF NOT EXISTS]
database_name;
Example: Suppose I want to create a
database named “Quiz”.
So the query will be
CREATE DATABASE IF NOT EXISTS QUIZ;
12. SHOW DATABASES;
You will see something like this-
13. DROP DATABASE [IF EXISTS]
database_name;
Example : Suppose I want to delete the
quiz database :
So the query will be
DROP DATABASE IF EXISTS Quiz;
14.
15. We have created Database in MySQL.
Now we will store data in Database.
We store data in Tabular format in MySQL.
That means we have to create tables to
store data.
16. CREATE TABLE [IF NOT EXISTS]
table_name( column_list
) type=table_type
Example: Suppose I want to create table
named “User_Password”
18. To
see the created table in the database
use query
SHOW TABLES;
To
see the description of a particular table
use query
DESCRIBE table_name;
19. INSERT INTO tbl_name () VALUES();
Example:
• INSERT INTO USER_PASSWORD
VALUES(„0705001‟,‟123456‟);
• INSERT INTO USER_PASSWORD
VALUES(„0705002‟,‟678901‟);
Username(varchar(6)) Password(varchar(6))
0705001 123456
0705002 678901
20. Alter table is used to change the structure
of the table
Suppose we forgot to add a column in the
USER_PASSWORD table.
Now we want to add a column name „type‟
in that table
21. ALTER
TABLE USER_PASSWORD
ADD COLUMN TYPE VARCHAR(5);
Using ALTER TABLE query:
• We can also drop column
• Rename the table
• Change the properties of a column
22. SELECT column_name1,column_name2...
FROM tables [WHERE conditions]
[GROUP BY group [HAVING
group_conditions]] [ORDER BY
sort_columns] [LIMIT limits];
Looking very complex
23. Mostsimple select statement
SELECT * FROM table_name;
• It selects the whole table;
SELECT COLUMN_NAME FROM TABLE
• Example:
SELECT USERNAME,TYPE FROM
USER_PASSWORD;
24. We do not always want to select the whole
table .Most of the time part of a table.
Example:
• SELECT PASSWORD,TYPE FROM
USER_PASSWORD WHERE USERNAME =
„0705001‟;
25. Primary key is used to distinguish two rows
in a table.
Now if I execute
INSERT INTO USER_PASSWORD
VALUES(„0705001‟,‟hello‟);
Username(varchar(6)) Password(varchar(6))
0705001 123456
0705001 hello
0705002 678901
26. Big problem.
One user two passwords. :O
We can avoid it by making USERNAME
column as primary key.
By making USERNAME column a primary
key we ensure that this column will have
all distinct value.
28. Used to change data in the table.
UPDATE table_name SET column_name
=
value WHERE (Some condition is true);
Suppose 0705001 wants to change his/her
password. The query will be :
UPDATE USER_PASSWORD SET
PASSWORD = „1234‟ WHERE
USERNAME = „0705001‟;
29. Usedto delete data in the table.
DELETE FROM table_name WHERE
(Some condition is true);
Suppose we want to throw out an
user(0*0*200) from our Database !!!
DELTE FROM USER_PASSWORD
WHERE USERNAME = „0*0*200‟;
30. These were very basic database queries.
Don‟t be worried if you did not understand
all the topics.
You will learn all this and many other
features in 3-1.