RDBMS Class 11 Notes | Unit 4 IT-802

RDBMS Class 11 Information Technology Notes covers RDBMS Terminology, MySQL Introduction, DDL and DML SQL Commands, Keys, Query Examples and all other important concepts with examples as per CBSE Syllabus. This RDBMS Class 11 Notes is specially designed for the students learning subject IT 802 Class. All the topics are prepared so concisely and in easy language that student can understands all concepts easily and secure full marks in their Board exams.

What is database?

Collection of logically related data that has been recorded, organized and made available for searching is called Database.

Use of database in real life applications

• Banking
• Online shopping
• Payroll
• Inventory management
• Loan and investment
• Reservation system And many more

What are the needs for a database?

• To manage large amount of data without redundancy (repetition).
• To manage large amount of data with lucidity (without complexity)
• To maintain data uniformly in different places or file
• Easy and convenient retrieval of data from any place or file
• Controlled data sharing at different user level

What is DBMS?

• DBMS stands for Database Management System.
• It is application software that can be used to create and manage database efficiently.
• it enable user or application to create, store, update, delete and retrieve data from database itself.
• It allows search and retrieve specific records from database
• It checks and ensures that only valid and accurate data is stored in database.
• Examples of DBMS are MySQL, Oracle, MongoDB, MS Access, MS SQL Server etc.

What are the advantages of DBMS?

• Reduction in Redundancy: Data in a DBMS is more concise because of the central repository of data. All the data is stored at one place. There is no repetition of the same data. This also reduces the cost of storing data on hard disks or other memory devices.
• Improved Consistency: The chances of data inconsistencies in a database are also reduced as there is a single copy of data that is accessed or updated by all the users.
• Improved Availability: Same information is made available to different users. This helps sharing of information by various users of the database.
• Improved Security: Though there is improvement in the availability of information to users, it may also be required to restrict the access to confidential information. By making use of passwords and controlling users’ database access rights, the DBA can provide security to the database.
• User Friendly: Using a DBMS, it becomes very easy to access, modify and delete data.  It reduces the dependency of users on computer specialists to perform various data related operations in a DBMS because of its user friendly interface.

What is RDBMS?

Stands for Relational Database Management System. It was developed by E.F. Codd at IBM 1970. It is used to organize collection of data as a collection of relations where each relation corresponds to a table of values. Each row in the table corresponds to a unique instance of data and each column name is used to interpret the meaning of that data in each row.

What are different RDBMS Terminologies? Explain.

Relation: a table is called relation. Another way we can say that collection of tuple is called relation.

Tuple: A row of table is called tuple. In another way we can say that a single record is called tuple

Attribute: a column of table is called attribute.

Domain: the data type of values in each column is called the Domain.

Keys | Candidate Key | Primary Key | Foreign Key | Alternate Key

column or a combination of columns which can be used to identify one or more rows (tuples) in a table is called a key of the table. There are 3 key constraints defined below:

Candidate key

• A column (attribute) or a group of columns which can be used as the primary key of a relation is called a Candidate key because it is one of the candidates available to be the primary key of the relation.
• A Candidate key is an attribute (or set of attributes) that uniquely identifies a row.
• A Primary Key is one of the candidate keys.

Primary Key

• One of the candidate key is designated as primary key.
• Primary key uniquely identifies tuples in relation.
• only one candidate key can become primary key.

Alternate Key

A candidate key of a table which is not selected as the primary key is called its Alternate Key.

What is Foreign Key?

• The key which is Primary key in another related table (relation) is called Foreign Key.
• A relation can have more than foreign keys.

What is MySQL? | Characteristics of MySQL

• MySQL is one of the most popular Relational Database Management System (RDBMS).
• MySQL was originally founded and developed in Sweden by David Axmark, Allan Larsson and Michael Widenius, who had worked together since the 1980s.

Characteristics of MySQL

• It is free and Open Source software which does not require to pay for its usage.
• It is easy to use, quick and reliable.
• It is platform independent software which works on many operating systems like
• Windows, UNIX, LINUX etc.
• It is compatible with many programming languages including JAVA, C++, PHP, PERL, etc.
• It can handle large amount of data very efficiently and accurately.

What is SQL?

SQL stands for Structured Query Language. It is developed to manage database. SQL enable us to create database, insert data, update data as per requirement and retrieve data.

What are the Categories of SQL Commands ?

All SQL commands are categorized in two types :

• Data Definition Language (DDL)
• Data Manipulation language (DML)

Data Definition Language (DDL)

• DDL is used to define structure and constraints of data
• It also defines key constraints, relationships between tables, and other data validation constraints.
• Example of DDL commands are:
  • CREATE DATABASE – creates a new database
  • CREATE TABLE – creates a new table
  • ALTER TABLE – modifies a table
  • DROP TABLE – deletes a table

Data Manipulation language (DML)

• DML is used to insert, modify and delete data in a database.
• Example of DML commands are:
  • SELECT – extracts data from a table
  • UPDATE – updates data in a table
  • DELETE – deletes data from a table
  • INSERT INTO – inserts new data into a table

What are the Datatypes used in MySQL?

Given table shows data types commonly used in SQL.

Data type	Use	Example
Char(n)	Fixed length character string. n denotes max no of characters.	Char(6) : sanjay, harish
Varchar(n)	Variable length character string. n denotes max no of characters.	Varchar(10): ram, arjun
Date	Date as YYYY-MM-DD	‘2022-07-23’
Integer	Whole number	45, 4539
Decimal(m,d)	Fixed point number. M denotes no of digits stored for values and d denotes no of decimal points.	Decimal(3,2): 34.89 Decimal(4): 2813
Float	Real number	456.23

Creating a Database

To create a database we will give CREATE DATABASE command.

Syntax

CREATE DATABASE <database name>;

Example:

Using a database

To open the database to work USE statements is used.

Syntax

USE <databasename>;

Example:

Viewing the current database

To view the name of current database we can use SELECT DATABASE(); command.

Syntax

SELECT DATABASE();

Example:

Create Table command

This command is used to create a new table or relation.

Syntax:

CREATE TABLE<table name>
(
<column 1><data type> [constraint] ,
<column 2><data type>[constraint],
<column 3><data type>[constraint]
);

Note: [Constraint] is optional

Example:

CREATE TABLE Item
(
Itemno char(5) primary key,
Itemname varchar(20),
Rate float NOT NULL,
Qty int
);

Screenshot:

Database Constraints | Not Null | Default | Primary Key | Unique Key | Foreign Key

Database enforces 5 types of constraints mentioned hereunder:

Not Null Constraint

Sometimes an attribute may not be allowed to leave blank. Hence Not Null constraints can be associated in this case.

Example:

CREATE TABLE TEACHER
(
Teacher_ID INTEGER,
First_NameVARCHAR(20) NOT NULL,
Last_NameVARCHAR(20),
Gender CHAR(1),
Date_of_Birth DATE,
Salary FLOAT,
);

Screenshot:

Default Constraint

To make a value bydefault  for an attribute Default constraint can be used.

CREATE TABLE TEACHER
(
Teacher_ID INTEGER,
First_NameVARCHAR(20) NOT NULL,
Last_NameVARCHAR(20),
Gender CHAR(1),
Date_of_Birth DATE,
Salary FLOAT DEFAULT 20000,
);

Screenshot:

Primary Key

it ensures followings when applied:

• Duplicate data is not allowed in the attribute.
• Attribute can not be left blank
• A relation can have only primary key

Example:

CREATE TABLE EMPLOYEE
(
Emp_ID INTEGER PRIMARY KEY,
Emp_NameVARCHAR(20) NOT NULL,
Gender CHAR(1),
Date_of_Birth DATE,
Salary FLOAT,
Dept varchar(20)
);

Screenshot:

Foreign Key

it ensures relationship between relations. The main purpose of this constraint is to check that data entered in one relation is consistent with the data entered in another relation.

Example:

Consider the following tables:
Item (Itemno, Iname, rate)
Order (Ono, Odate, Ino, qty, total)

Here in this example Ino is the foreign key that references Ino of Item table which is Primary key.

The SQL command for making Ino to foreign key in Order table is as follows:

Create Order
(
Ono int Primary Key,
Odate date,
Itemno int,
Qty int,
Total int,
FOREIGN KEY (Itemno) REFERENCES Item (Itemno)
);

Screen Shot:

Unique Key

it ensures followings when applied:

• Duplicate data is not allowed in the attribute.
• A relation can have multiple unique keys

Example:

CREATE TABLE EMPLOYEE
(
Emp_ID INTEGER PRIMARY KEY,
Emp_NameVARCHAR(20) NOT NULL,
Gender CHAR(1),
Date_of_Birth DATE,
Salary FLOAT,
Dept varchar(20) UNIQUE
);

Screenshot:

Viewing Structure of table | DESCRIBE command

• We can use DESCRIBE or DESC command to view the structure of a table as mentioned in CREATE TABLE command.
• It display table structure including attributes, data types and constraints .

Syntax:

DESCRIBE <table name>;
Or
DESC <table name>;

Example:

DESCRIBE EMPLOYEE;

ScreenShot

Drop table

This command is used to delete a table completely from database. It deletes structure and data both of table from database.

Syntax:

DROP TABLE <table name>;

Example:

DROP TABLE Orders;

How to modify structure of table? | ALTER TABLE Command in SQL

Alter table

It is used to modify structure of a table. Following are the alteration can be done using this command:

Adding a column

we can add a new column in existing table.

Example:

ALTER TABLE Item ADD date_of_purchase date NOT NULL;

Dropping a column

A column can be dropped using alter table command as given below:

Example:

ALTER TABLE Item DROP qty;

Modifying a table:

A column can also be modified using Alter Table command as given below:

ALTER TABLE item MODIFY qty SET DEFAULT 100;

Screenshot:

How to add Primary Key?

How to drop primary key?

ALTER TABLE Item DROP Primary key;

Data Manipulation Language | DML

• DML is used to insert, modify and delete data in a database.
• Example of DML commands are:
  • SELECT – extracts data from a table
  • UPDATE – updates data in a table
  • DELETE – deletes data from a table
  • INSERT INTO – inserts new data into a table

Insert command

This command is used to insert a tuple in a relation. We must specify the name of the relation in which tuple is to be inserted and the values. The values must be in the same order as specified during the Create Table command.

Syntax:

INSERT INTO <tablename> VALUES (<values >);

Example:

Inserting values in table Item (Ino, Iname, Rate, Qty)

INSERT INTO Item Values (1, ‘soap’,44,120);

Screenshot:

Update command

Update command is used to modify the attribute values of one or more tuples in a table.

Syntax:

UPDATE <tablename>
SET  <expression>
WHERE <criteria>

Example:

UPDATE Item
SET Rate = 30
WHERE itemno = ‘i0001’;

Screenshot:

Delete command

To delete one or more tuples (rows) in a realtion DELETE command is used.

Syntax:

DELETE FROM <tablename>
WHERE <criteria>;

Example:

DELETE FROM item WHERE itemno = ‘i0002’;

Screenshot:

Select command

Select command is used to access or retrieve specific or complete set of records from database.

Syntax:

SELECT <attribute list> FROM <table name>;

Query1: Display all records from Item table.

Code:

Select * from item;

Screenshot:

Query2: Display itemname with its rate from item table.

Code:

Select itemname,rate from item;

Screenshot:

Query3: display name of items which rate is more than 100.

Code:

Select itemname from item where rate > 100;

Screenshot:

Query4: display item records which name begins with s.

Code:

Select * from item where itemname like ‘s%’;

Screenshot:

Query5: retrieve item details which rate is less than 100 and qty is more than 100.

Code:

Select * from item where rate < 100 and qty > 100;

Screenshot:

DISTINCT Command

DISTINCT command is used to eliminate repeated data of a column when display using SELECT command

Syntax:

SELECT DISTINCT(field that contains repeated data) FROM <table name>
WHERE <criteria>;

Example

Screenshot

WHERE clause

• WHERE clause act as a Filter while manipulate records in SQL.
• Where clause is used to define Criteria for the records to be retrieved.
• It can be used with any DML command such as SELECT, DELETE and UPDATE.
• To define criteria various operators like Arithmetic, Range or Comparison operators are used in WHERE clause.

Syntax:

SELECT <field(s)> FROM <table name>
WHERE <criteria>;

Example:

Query5: retrieve item details which rate is less than 100 and qty is more than 100.

Code:

Select * from item where rate < 100 and qty > 100;

Screenshot:

Example:

DELETE FROM item WHERE itemno = ‘i0002’;

Screenshot:

Operators used with WHERE clause

• Arithmetic operators
• Relation operators
• Logical operators
• BETWEEN operators
• IN operators
• LIKE operators

Arithmetic operators

• We can use arithmetic operators to define expressions in DML SQL commands.
• Arithmetic operators are used with numeric values.
• Following table depicts various arithmetic operators:

Arithmetic Operator	Description
+	For adding values
–	For subtracting values
*	For multiplying values
/	For dividing values
%	For finding remainders

Example:

Relational operators

• We can use Relational operators to compare values in SQL.
• Mostly used to define criteria in WHERE clause to filter records.
• Following table depicts various Relational operators:

Relational Operator	Description
=	Equal to
>	Greater than
<	Lesser than
>=	Greater than equal to
<=	Lesser than equal to
!= or <>	Not equal to

Example:

Logical operators

• Logical operators are used to combine multiple criteria/expression in DML SQL commands
• Mostly used to combine criteria in WHERE clause to filter records.
• Following table depicts various Logical operators:

Logical Operator	Description
AND	Returns true when all criteria/expressions are true
OR	Returns true when at least a criteria/expression is true
NOT	Negates the result

BETWEEN operator

• It is used to define range of values for a particular field in WHERE clause.
• It can be used to define range of numerical or chronological values
• It includes upper and lower bound given in the range.

Example:

IN operator

• It is used to set multiple text comparison for a particular field in WHERE clause.
• It can only be used for text comparision.

Example:

LIKE operator

• It is used to define string expressions (pattern matching) in WHERE clause.
• It uses different wildcards (described in image given below) to define string expression.

Wildcard	Description
%	Used to match the occurrence of set of characters of any length
_	Underscore used to match occurrence of any single character

Example:

Order by clause

• Used to display records in sequential manner in data resultset retrieved by WHERE clause.
• Bydefault displays records in ascending order.
• Keyword ASC (Ascending) or DESC (descending) can be used with order by to arrange the data resultset.

Example: