Introduction to dbms

Presentation
by
Prof.Ms.V. Umamaheswari,
Department of IT,
Bon secours college for women,
Thanjavur.

 DBMS Stands as Database management
System
 Database + Management System
 Database is a Collection of Data
 Management System is a Set of Program to
Store and Retrieve those Data

Database Management System is a Collection of
Data and Set of Program to access and Store those
Data in an easy and efficient Manner.
 DBMS is a Software
 Example : MySQL, Oracle etc…are popular
Commercial DBMS Used in Different
Application

Previously data is store in files
Drawback :
1.Data redundancy and inconsistency
Multiple file format, Duplication of information in
different files Difficulty in access in data
2. Difficulty in access in data
Need to write a new program to carry out each tasks
3.Data isolation
Multiple files &formats
4.Data Security
5.Transaction Problems
So database system offer solution to all these problems

 DDL –Data Definition Languages
 DML – Data Manipulation languages
 DCL – Data Control languages

• It is used for Defining & Modifying the Data and it
structures.
• It is used to Build and Modifying the Structure of your tables.
Commands:
 CREATE - used to create objects in the database
 ALTER - used to alters the structure of the database
 DROP - used to delete objects from the database
 TRUNCATE - used to remove all records from a table,
including all spaces allocated for the records are removed
 COMMENT - used to add comments to the data dictionary
 RENAME - used to rename an object

Data Manipulation Language (DML) statements are used to
manage data within schema objects.
 SELECT - It retrieves data from a database
 INSERT - It inserts data into a table
 UPDATE - It updates existing data within a table
 DELETE - It deletes all records from a table, the space
for the records remain
 MERGE - UPSERT operation (insert or update)
 CALL - It calls a PL/SQL or Java subprogram
 EXPLAIN PLAN - It explains access path to data
 LOCK TABLE - It controls concurrency

• The Data Control Language (DCL) is used to
control privilege in Database.
• To perform any operation in the database,
such as for creating tables, sequences or
views we need privileges.
Privileges are of two types,
 System - creating a session, table, etc. are all
types of system privilege.
 Object - any command or query to work on
tables comes under object privilege.
DCL is used to define two commands.
These are:

 NOT NULL constraint
Ensures that column does not accept nulls
 UNIQUE constraint
Ensures that all values in column are unique
 DEFAULT constraint
Assigns value to attribute when a new row is
added to table
 CHECK constraint
Validates data when attribute value is entered

 When primary key is declared, DBMS
automatically creates unique index
 Often need additional indexes
 Using CREATE INDEX command, SQL
indexes can be created on basis of any selected
attribute
 Composite index
Index based on two or more attributes
Often used to prevent data duplication

 Adding table rows
 Saving table changes
 Listing table rows
 Updating table rows
 Restoring table contents
 Deleting table rows
 Inserting table rows with a select subquery

 Whenever we don’t have a value, we can put a NULL
 Can mean many things:
 Value does not exists
 Value exists but is unknown
 Value not applicable
 Etc.
 The schema specifies for each attribute if can be null
(nullable attribute) or not
 How does SQL cope with tables that have NULLs ?

 If x= NULL then 4*(3-x)/7 is still NULL
 If x= NULL then x=“Joe” is UNKNOWN
 In SQL there are three Boolean values:
FALSE = 0
UNKNOWN = 0.5
TRUE = 1

C1 AND C2 = min(C1, C2)
C1 OR C2 = max(C1, C2)
NOT C1 = 1 – C1
SELECT *
FROM Person
WHERE (age < 25) AND
(height > 6 OR weight > 190) E
E.g.
age=20
height=NULL
weight=200

Unexpected behavior:
SELECT *
FROM Person
WHERE age < 25 OR age >= 25
Some Persons are not included !

Can test for NULL explicitly:
 x IS NULL
 x IS NOT NULL
SELECT *
FROM Person
WHERE age < 25 OR age >= 25 OR age
IS NULL
Now it includes all Persons

Introduction to dbms

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