RDBMS with MySQL

© People Strategists - Duplication is strictly prohibited -www.peoplestrategists.com


Overview of Database Models

Basic Definitions:

Data: Known facts that can be recorded and have an implicit meaning.

Table: A collection of data elements organized in terms of rows and columns.

Record/Tuple: A single entry in a table is called a record or a tuple.

Field/Attributes: A table consists of several records and each record can be broken intovarious smaller entities known as fields.

Database: A collection of related data.

Database Management System (DBMS): A software system that facilitates the creationand maintenance of a computerized database.

Database System: The DBMS software together with the data itself. Sometimes, theapplications are also included.



Database Models:

Define how the logical structure of a database is modeled.

Are fundamental entities to introduce abstraction in a DBMS.

Define how different parts of data are connected to each other and how these are processed and stored inside the system.



Types of Database Models

Object-oriented Model

Relational Model

Network Model

Hierarchical Model


Overview of Database Models (Contd.)

Hierarchical Model:

The data is organized in a tree structure.

There is a hierarchy of parent and child data segments.

A parent can have many children, but a child can have a single parent.

This structure allows one-to-many relationship between two types of data.



Example of Hierarchical Model:



Network Model:

Entities are organized in a graph, in which some entities can be accessed through several path.

A parent can have multiple children and a child can also have multiple parents.

This structure allows many-to-many relationship between two types of data.



Example of Network Model:



Relational Model:

All data is represented in terms of tuples, grouped into relations.

The tables or relations are related to each other.

A database organized in terms of the relational model is a relational database.

The purpose of the relational model is to provide a declarative method for specifying data and queries.



Example of Relational Model:



Object-Oriented Model:

Both data and their relationship are contained in a single structure known as an object.

An object includes information about relationship between the facts within the object, as well as information about its relationship with other objects.

An object is the abstraction of the real-word entity. An object represents only one occurrence of an entity.

Attributes describe the property of an object.

Objects that are similar in characteristics are grouped in a class.



Example of Object-Oriented Model :

Employee

Name

ID

Salary


Introduction to RDBMS

A Relational Database Management System (RDBMS):

Is a database management system based on relational model introduced by E.F Codd.

Represents data in terms of tuples(rows).

Is used to manage Relational database.

Relational Database:

Is a collection of organized set of tables from which data can be accessed easily.

Consists of number of tables and each table has its own primary key.


Database Keys

Super Key is defined as a set of attributes within a table that uniquely identifies each record within a table. Super Key is a superset of Candidate key.

A Candidate Key:o Is a subset of a super key.o Is a single field or the least combination of fields that uniquely identifies each record in

the table. The least combination of fields distinguishes a candidate key from a super key.

o Must contain unique values.

o Must not contain null values.

o Contains the minimum number of fields to ensure uniqueness.

o Must uniquely identify each record in the table.


Database Keys

Example of Candidate Key:


Database Keys (Contd.)

Primary Key:

Is a candidate key that is most appropriate to be the main reference key for the table.

Is used throughout the database to help establish relationships with other tables.

Must contain unique values, must never be null and should uniquely identify each record in the table.



Example of Primary Key:



A foreign Key is generally a primary key from one table that appears as a field in another table, where the first table has a relationship to the second.

For example, if we had a table A with a primary key X that linked to a table B where X was a field in B, then X would be a foreign key in B.



Example of Foreign Key:



Alternate key is any candidate key which is not selected to be the primary key.

Compound key (also called a composite key or concatenated key) is a key that consists of 2 or more attributes.


Normalization

The main goal of Database Normalization is to restructure the logical data model of a database to:

Eliminate redundancy

Organize data efficiently

Reduce the potential for data anomalies

Data Anomalies:

Are inconsistencies in the data stored in a database as a result of an operation, such as update, insertion, and/or deletion.

May arise when have a particular record stored in multiple locations and not all of the copies are updated.

Can be prevented by implementing normalization.


Normalization (Contd.)

Dependencies:

Multivalued Attributes (or repeating groups): Non-key attributes or groups of non-key attributes, the values of which are not uniquely identified by (directly or indirectly) (not functionally dependent on) the value of the Primary Key (or its part).

Example:

STUDENT

Stud_ID Name Course_ID Units

101 Lennon MSI 250 3.00

101 Lennon MSI 415 3.00

125 Johnson MSI 331 3.00



Partial Dependency: When a non-key attribute is determined by a part, but not the whole, of a composite primary key.

Example:



Transitive Dependency: When a non-key attribute determines another non-key attribute.

Example:



Normalization rules are divided into the following normal forms:

First Normal Form (1NF)

Second Normal Form (2NF)

Third Normal Form (3NF)

Boyce and Codd Normal Form (BCNF)



Requirements to satisfy 1NF:

Each table has a primary key.

The values in each column of a table are atomic (No multi-value attributes allowed).

There are no repeating groups: two columns do not store similar information in the same table.



Example of 1NF:

The Student Table




All requirements for 1NF must be met.

Redundant data across multiple rows of a table must be moved to a separate table.

o The resulting tables must be related to each other by use of foreign key.



Example of 2NF:

New Student Table

New Subject Table





Eliminate fields that do not depend on the primary key;o That is, any field that is dependent not only on the primary key but also on another

field must be moved to another table.



Example of 3NF:

Student_Detail Table

New Student_Detail Table

Address Table



Requirements to satisfy BCNF:


For each functional dependency ( X -> Y ), X should be a super Key.

Example:

Consider the relationship, R(E, F, G, H) and the dependencies E->FGH, FG->EH, and

H->F. This relationship is already in 3NF. Keys are E and FG. Thus, in FD E->FGH, E is the super key. In second relation, FG->EH, FG is also a key. But, in H->F, H is not a key.

Thus, we can break R into R1 and R2 as shown below:

R1(E,H,G) and R2(H,F)


ER Diagrams

ER Diagrams:

Were proposed by Peter Chen in 1976.

Are widely used in database design.

Represent conceptual level of a database system.

Describe entities and their relationships in high level.


ER Diagrams (Contd.)

Basic Concepts Required for ER Diagrams:

Entity – An abstraction of similar things, e.g. cars, students, and employees.o An entity set contains many entities.

Attributes: Common properties of the entities in entity sets.

Relationship: Specifies the relations among entities from two or more entity sets.



Symbols and Notations:

Symbols Notations

Entity

Relationship

Attribute



Symbols Notations

Weak Entity

Weak Entity Relationship

Multivalued Attribute



Symbols Notations

Key Attribute

Composite Attribute



Types of relationship that exist between Entities:

Binary Relationship: Means relation between two entities.

Recursive Relationship: An Entity is related to itself.

Ternary Relationship: Relationship of degree three.



Binary relationship is further divided into three types:

1. One-to-one



2. One-to-many

3. Many-to-one



An ER Diagram:


Features of MySQL

Some of the MySQL features are:

Open source: MySQL source code is available on Internet that can be modified by anyone.

Portable: It is compatible with various operating systems, such as Windows, Linux, and Mac OS. It can also run on different types of system architectures.

Scalable: It is capable of managing small as well as large databases.

Reliable: It can deliver high performance under varying conditions.


Features of MySQL

Easy to use: MySQL provides Graphical User Interface (GUI) as well as Command line User Interface (CUI). Database Developers can choose the most appropriate interface for interacting with database.

Secure: Only authorized users can access the database. This is possible by creating dedicated accounts for users.

High availability: MySQL supports replication. Various copies of server are available on the same computer or on different computers. Replication ensures 24*7 availability of the database server across different locations. A large number of client requests can be handled uninterruptedly.


MySQL Data Types

MySQL uses many different data types broken into three categories:

Numeric

Date and time

String


MySQL Data Types (Contd.)

Numeric Data Types

Data type Description Range for signed integers

Range for unsigned integers

Storage in bytes

INT A normal-sized integer that can be signed or unsigned. You can specify a width of up to 11 digits.

–2,147,483,648 to 2,147,483,647

0 to 4294967295

4

TINYINT A very small integer that can be signed or unsigned. You can specify a width of up to 4 digits.

–128 to 127 0 to 255 1



Data type Description Range for signed integers

Range for unsigned integers

Storage in bytes

SMALLINT A small integer that can be signed or unsigned. You can specify a width of up to 5 digits.

–32,768 to 32,767 0 to 65535 2

MEDIUMINT A medium-sized integer that can be signed or unsigned. You can specify a width of up to 9 digits.

–83,88,608 to 83,88,607 0 to 16777215 3

BIGINT A large integer that can be signed or unsigned. You can specify a width of up to 20 digits.

–9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

0 to 18446744073709551615

8



Data type Description Range Stores Storage in bytes

FLOAT(M,D)A floating-point number that cannot be unsigned. You can define the display length (M) and the number of decimals (D).

–3.402823466E+38 to –1.175494351E–38, 0 and 1.175494351E–38 to 3.402823466E+38

Fractional value with floating single-precision

4

DOUBLE(M,D) A double precision floating-point number that cannot be unsigned. You can define the display length (M) and the number of decimals (D).

–1.7976931348623157E+308 to –2.2250738585072014E–308, 0 and 2.2250738585072014E–308 to 1.7976931348623157E+308

Fractional value floating double-precision and scale

8



Date and Time Types:

DATE: A date in YYYY-MM-DD format, between 1000-01-01 and 9999-12-31.

DATETIME: A date and time combination in YYYY-MM-DD HH:MM:SS format, between 1000-01-01 00:00:00 and 9999-12-31 23:59:59.

TIMESTAMP: A timestamp between midnight, January 1, 1970 and sometime in 2037.

TIME: Stores the time in HH:MM:SS format.

YEAR(M): Stores a year in 2-digit or 4-digit format.



String Types:

CHAR(M): A fixed-length string between 1 and 255 characters in length. Defining a length is not required, default is 1.

VARCHAR(M): A variable-length string between 1 and 255 characters in length. You must define a length when creating a VARCHAR field.

BLOB or TEXT: A field with a maximum length of 65535 characters. Binary Large Objects used to store large amounts of binary data, such as images or other types of files.

TINYBLOB or TINYTEXT: A BLOB or TEXT column with a maximum length of 255 characters.



MEDIUMBLOB or MEDIUMTEXT: A BLOB or TEXT column with a maximum length of 16777215 characters.

LONGBLOB or LONGTEXT: A BLOB or TEXT column with a maximum length of 4294967295 characters.

ENUM: Creates a list of items from which the value must be selected.


Introduction to DQL, DDL, DML, and DCL

DQL:

Stands for Data Query Language.

Is used to display the data in a table or tables.

Supports the SQL command, SELECT.



DDL:

Stands for Data Definition Language.

Statements are used to define the database structure or schemas.

Supports statements, such as CRATE, ALTER, DROP, TRUNCATE, COMMENT, and RENAME.



DML:

Stands for Data Manipulation Language.

Is used for managing data within database objects.

Supports statements, such as INSERT, UPDATE, DELETE, MERGE, CALL, EXPLAIN PLAN, and LOCK TABLE.



DCL:

Stands for Data Control Language.

Is used to create roles, permissions, and referential integrity.

Controls access to database by securing it.

Supports statements, such as GRANT and REVOKE.


DDL

Creating Database

CREATE DATABASE statement is used to create databases or schemas.

Syntax:

CREATE {DATABASE|SCHEMA} [IF NOT EXISTS] <db_name>;

Examples:

CREATE DATABASE IF NOT EXISTS Hotels_Chain;

CREATE DATABASE IF NOT EXISTS Sample_db;


DDL

Accessing Database

A database acts as a container for related database objects.

To perform any operation on a database object, you first need to access the database.

USE statement is used to access databases or schemas.

Syntax: USE <db_name>;

Example: USE Hotels_Chain;


DDL

Accessing Database

SHOW DATABASES statement is used to view a list of all the databases in the MySQL server.

Usage:

SHOW DATABASES;

Output:


DDL

Deleting Database

DROP DATABASE Statement is used to drop all the tables in the database and then, deleting the database.

Syntax:

DROP {DATABASE|SCHEMA} [IF EXISTS] <db_name>;

Example:

DROP DATABASE IF EXISTS Sample_db;

SHOW DATABASES;


DDL

Output:


DDL (Contd.)

CREATE TABLE Statement:

Is used to create tables.

Syntax: CREATE TABLE [IF NOT EXISTS] <table_name>

(

col1_name datatype [NOT NULL|NULL] [DEFAULT value] [AUTO_INCREMENT] [UNIQUE] [PRIMARY KEY],

col2_name datatype [NOT NULL|NULL] [DEFAULT value] [AUTO_INCREMENT] [UNIQUE] [PRIMARY KEY],

....

)


DDL (Contd.)

Example of CREATE TABLE Statement:

Products TableCREATE TABLE IF NOT EXISTS Products

(

Product_ID int NOT NULL,

Product_Name varchar(45) NOT NULL,

Quantity_In_Hand int NOT NULL,

Re_Order_Quantity INT NULL,

Re_Order_Level INT NULL,

Price INT NULL

);


DDL (Contd.)

Customers TableCREATE TABLE IF NOT EXISTS Customers

(

Customer_ID INT NOT NULL,

FirstName VARCHAR(50) NOT NULL,

LastName VARCHAR(50) NOT NULL,

Address VARCHAR(80),

City VARCHAR(30),

Postal_Code INT

);


DDL (Contd.)

Viewing Data about Tables

DESCRIBE/DESC statement is used to view the detailed data about all the columns of the table, such as name of the column, data type, and default value.

Syntax:

DESCRIBE table_name;

or

DESC table_name;


DDL (Contd.)

For example, you can view the detailed column data of Products and Customers table, as shown follows:

DESCRIBE Products;

Output:


DDL (Contd.)

DESC Customers;

Output:


DDL (Contd.)

Altering a Table

The structure of a table is defined while creation.

Later, you may often need to alter its structure.

ALTER TABLE is used to alter a table.

This statement can be used to add a new column, change the name or data type of an existing column, drop a column, add or remove constraints on existing columns, and much more.


DDL (Contd.)

Adding a Column to Table:

Use of ADD clause.

Example:

ALTER TABLE Customers ADD Gender VARCHAR(30);

You can view the structure of Customers table using DESC statement:

DESC Customers;


DDL (Contd.)

Output:


DDL (Contd.)

Changing Column Name:

Use of CHANGE COLUMN clause.

Example:

ALTER TABLE Customers CHANGE COLUMN Gender Sex

VARCHAR(30);

DESC Customers;


DDL (Contd.)

Output:


DDL (Contd.)

Dropping a Column from Table:

Use of DROP COLUMN clause.

Example:

ALTER TABLE Customers DROP COLUMN Sex;

DESC Customers;


DDL (Contd.)

Output:


DDL (Contd.)

Adding a PRIMARY KEY Constraint to Table:

Syntax:ALTER TABLE <table_name>

ADD PRIMARY KEY(primary_key_column);

Example:

ALTER TABLE Customers ADD PRIMARY KEY (Customer_ID);

DESC Customers;


DDL (Contd.)

Output:


Working with Keys

PRIMARY KEY constraint can be added to a table:

While creating the table.

After creating the table.


Working with Keys

Example for adding PRIMARY KEY constraint while creation of a table:DROP TABLE Products;

CREATE TABLE IF NOT EXISTS Products

(

Product_ID int NOT NULL,

Product_name varchar(45) NOT NULL,

Quantity_in_hand int NOT NULL,

Re_order_quantity INT NULL,

Re_order_level INT NULL,

Price INT NULL,

PRIMARY KEY(Product_ID)

);

DESC Products;


Working with Keys

Output:


Working with Keys (Contd.)

Example of PRIMARY Key Constraint on Multiple Columns (Composite key):

CREATE TABLE Persons

(

P_Id int NOT NULL,

LastName varchar(255) NOT NULL,

FirstName varchar(255),

Address varchar(255),

City varchar(255),

CONSTRAINT pk_PersonID PRIMARY KEY (P_Id,LastName)

);

DESC Persons;



Output:



Example for dropping a PRIMARY Key Constraint:

ALTER TABLE Persons

DROP PRIMARY KEY;

DESC Persons;

Output:



FOREIGN KEY Constraint can be added to a table using :

CREATE TABLE statement

ALTER TABLE statement



Example using CREATE TABLE statement:CREATE TABLE IF NOT EXISTS Customer_Order (

Order_ID INT NOT NULL,

Product_ID INT NOT NULL,

Customer_ID INT NOT NULL,

Quantity_Ordered INT NOT NULL,

CONSTRAINT fk1 FOREIGN KEY (Product_ID)

REFERENCES Products(Product_ID),

CONSTRAINT fk2 FOREIGN KEY (Customer_ID)

REFERENCES Customers(Customer_ID) );

DESC Customer_Order;



Output



Example to create FOREIGN KEY constraints using ALTER TABLE statement:

CREATE TABLE IF NOT EXISTS Categories (

Cat_ID INT NOT NULL PRIMARY KEY,

Cat_Name VARCHAR(50) NOT NULL,

Cat_Desc TEXT );

CREATE TABLE ProductsDemo (

PID INT NOT NULL PRIMARY KEY,

PName VARCHAR(50) NOT NULL,

PPrice DECIMAL NOT NULL,

CatID INT NOT NULL );



ALTER TABLE ProductsDemo

ADD CONSTRAINT fk_ProductsDemo

FOREIGN KEY (CatID)REFERENCES Categories(Cat_ID);

DESC ProductsDemo;

Output:



Removing a FOREIGN KEY Constraint

Syntax of ALTER statement to drop a foreign key:ALTER TABLE table_name

DROP FOREIGN KEY constraint_name

To identify the constraint name of the foreign key the SHOW CREATE TABLE statement can be used.

Example:

SHOW CREATE TABLE Products_Demo;



Output:

The name of the foreign key constraint in ProductsDemo table is, fk_ProductsDemo.



Example to drop the constraint using Alter Table statement:

ALTER TABLE ProductsDemo

DROP FOREIGN KEY fk_ProductsDemo;

desc ProductsDemo;

Output:


DDL (Contd.)

DROP TABLE Statement:

Removes one or more tables including indexes and privileges.

Cannot be rolled back.

Syntax:

DROP TABLE [IF EXISTS] <table_name>

Example:

DROP TABLE IF EXISTS ProductsDemo;


Truncating Table

TRUNCATE TABLE Statement:

Removes all records from a table.

Operation cannot be rolled back.

Syntax:

TRUNCATE TABLE <table_name>;


CRUD Operations with Database

INSERT Statement:

Inserts records into a table.

Syntax:

INSERT INTO <table_name> ( col1, col2,...colN )

VALUES( value1, value2,...valueN );


CRUD Operations with Database (Contd.)

Example:INSERT INTO

Products(Product_ID,Product_Name,Quantity_in_hand,Re_or

der_quantity,Re_order_level,Price) VALUES(1,'Red Rugs

Carpets',400,500,400,800);INSERT INTO


der_quantity,Re_order_level,Price) VALUES(2,'Soft Silk

carpets',300,600,700,5000);INSERT INTO


der_quantity,Re_order_level,Price) VALUES(3,'Black Rugs

Carpets',500,400,500,7000);

Inserting data into Products table



INSERT INTO Products(Product_ID,Product_Name,Quantity_in_hand,Re_order_quantity,Re_order_level,Price) VALUES(4,'Black Silk Sofa',100,600,700,7000);

INSERT INTO Products(Product_ID,Product_Name,Quantity_in_hand,Re_order_quantity,Re_order_level,Price) VALUES(5,'Red Velvet Sofa',120,500,700,10000);

INSERT INTO Products(Product_ID,Product_Name,Quantity_in_hand,Re_order_quantity,Re_order_level,Price) VALUES(6,'Pink Rugs Carpets',400,200,500,2000);



INSERT INTO Products(Product_ID,Product_Name,Quantity_in_hand,Re_order_quantity,Re_order_level,Price) VALUES(7,'Black Silk carpets',300,500,600,4000);INSERT INTO Products(Product_ID,Product_Name,Quantity_in_hand,Re_order_quantity,Re_order_level,Price) VALUES(8,'Hard Rugs Carpets',500,600,700,5000);

INSERT INTO Products(Product_ID,Product_Name,Quantity_in_hand,Re_order_quantity,Re_order_level,Price) VALUES(7,'Black Silk carpets',300,500,600,4000);



INSERT INTO


der_quantity,Re_order_level,Price) VALUES(8,'Hard Rugs

Carpets',500,600,700,5000);INSERT INTO


der_quantity,Re_order_level,Price) VALUES(9,'Pink Silk

Sofa',100,400,500,6000);INSERT INTO


der_quantity,Re_order_level,Price) VALUES(10,'Black

Velvet Sofa',120,600,700,5000);



INSERT INTO Customers(Customer_ID,FirstName,LastName,Address,City,Postal_Code) VALUES(1,'Peter','James','Torikatu 46','Oulu',90110);INSERT INTO Customers(Customer_ID,FirstName,LastName,Address,City,Postal_Code) VALUES(2,'Wellington','Importadora','rua do Mercado 12','Resende',8737);INSERT INTO Customers(Customer_ID,FirstName,LastName,Address,City,Postal_Code) VALUES(3,'White','Markets','305 Ave Suite','Resende',8737);INSERT INTO Customers(Customer_ID,FirstName,LastName,Address,City,Postal_Code) VALUES(4,'Andrew','Louise','67 Mercado','Resende',8737);INSERT INTO Customers(Customer_ID,FirstName,LastName,Address,City,Postal_Code) VALUES(5,'Harry','James','Torikatu 59','Oulu',90110);

Inserting data into Customers table



INSERT INTO Customers(Customer_ID,FirstName,LastName,Address,City,Postal_Code) VALUES(6,'Wilman','Kala','Keskuskatu 45','Helsinki',21240);INSERT INTO Customers(Customer_ID,FirstName,LastName,Address,City,Postal_Code) VALUES(7,'Wolski','Zbyszek','ul. Filtrowa68','Poland',1012);INSERT INTO Customers(Customer_ID,FirstName,LastName,Address,City,Postal_Code) VALUES(8,'Andy','James','607 Ave Suite','Poland',1012);INSERT INTO Customers(Customer_ID,FirstName,LastName,Address,City,Postal_Code) VALUES(9,'Nisha','Mathew','407 ','Resende',8737);INSERT INTO Customers(Customer_ID,FirstName,LastName,Address,City,Postal_Code) VALUES(10,'Harry','James','Torikatu 79','Helsinki',21240);



Insert into customer_order(Order_ID,Product_ID,Customer_ID,Quantity_Ordered) values(1,1,1,10);Insert into customer_order(Order_ID,Product_ID,Customer_ID,Quantity_Ordered) values(2,1,1,20);Insert into customer_order(Order_ID,Product_ID,Customer_ID,Quantity_Ordered) values(3,2,1,10);Insert into customer_order(Order_ID,Product_ID,Customer_ID,Quantity_Ordered) values(4,2,2,30);Insert into customer_order(Order_ID,Product_ID,Customer_ID,Quantity_Ordered) values(5,3,2,10);

Inserting data into Customer_Order table



Insert into customer_order(Order_ID,Product_ID,Customer_ID,Quantity_Ordered) values(6,3,3,50);Insert into customer_order(Order_ID,Product_ID,Customer_ID,Quantity_Ordered) values(7,4,3,60);Insert into customer_order(Order_ID,Product_ID,Customer_ID,Quantity_Ordered) values(8,4,4,70);Insert into customer_order(Order_ID,Product_ID,Customer_ID,Quantity_Ordered) values(9,5,4,80);Insert into customer_order(Order_ID,Product_ID,Customer_ID,Quantity_Ordered) values(10,5,5,60);


SelectionProjection

Table 1 Table 2

Table 1Table 1

Join


Capabilities of SELECT Statement



SELECT Statement:

Can fetch records from a one or more tables at a time.

Uses any condition with WHERE clause.

Syntax:

SELECT field1, field2,...fieldN table_name1, table_name2...

[WHERE Clause]

[LIMIT N]

LIMIT attribute can limit the number of returned records.



Example 1: Retrieving all the records from Products table.

select * from Products;

Output:



Example 2: Retrieving details of the product having ID as 1.

select * from products where Product_ID=1;

Output:



Example 3: Retrieving details of Black Velvet Sofa.

select * from products where Product_name='Black Velvet

Sofa';

Output:



Example 4: Retrieving price of Black Velvet Sofa.

select Product_ID,Product_name,Price from products where

Product_name='Black Velvet Sofa';

Output:



Example 5: Retrieving all records of Customers table.

select * from Customers;

Output:



Example 6: Retrieving details of customers residing in Poland.

select * from customers where city='Poland';

Output:



UPDATE Statement:

Can update one or more field altogether.

Can specify any condition using WHERE clause.

Can update values in a single table at a time.

Syntax:

UPDATE <table_name> SET col1=new_value1,

col2=new_value2

[WHERE Clause]



Example 1: Updating price of Black Silk Sofa to 9000.

UPDATE Products

SET Price=9000

WHERE Product_name='Black Silk Sofa';

select * from products WHERE Product_name='Black Silk Sofa';

Output:



Example 2: Updating address of Andrew Louise to 56 Ave Suite.

update customers

set Address='56 Ave Suite'

where firstname='Andrew' and lastname='louise';

select * from customers

where firstname='Andrew' and lastname='louise';

Output:



DELETE FROM Statement:

Deletes records from a table.

Can specify any condition using WHERE clause.

Can delete records from a single table at a time.

If no WHERE condition is specified, all rows will be removed. After performing a DELETE operation you need to COMMIT or ROLLBACK the transaction to make the change permanent or to undo it.

Syntax:

DELETE FROM <table_name>

[WHERE Clause]



Example: Removing record for the customer with ID “7”.

DELETE FROM Customers WHERE Customer_ID=7;

select * from customers;

Output:


Aggregate Functions

MySQL supports various aggregate functions. Some of these are:

Function Description Example

AVG() Returns the average value of the argument.

SELECT AVG(Price)

average_buy_price

FROM products;

COUNT() Returns a count of the number of rows returned.

SELECT COUNT(*) AS Total

FROM products;

MAX() Returns the maximum value in a set of values.

SELECT MAX(Price)

highest_price

FROM Products;


Aggregate Functions (Contd.)

Function Description Example

MIN() Returns the minimum value in a set of values.

SELECT MIN(Price)

lowest_price

FROM Products;

SUM() Returns the sum of a set of values.. SELECT sum(10+20+30)

DemoSum;

CONCAT() Returns the concatenated string. SELECT concat('James','

Peter') Name;



GROUP BY Clause:

Is used with the SELECT statement to group rows into subgroups by the one or more values of columns or expressions.

Can be used with aggregate functions to provide means of grouping the result dataset by certain database table column(s).



Example 1: Retrieving the cities and total number of customers belonging to those cities and having IDs less than 8.select Count(Customer_ID) Total_Customers,City from Customers

Group by city;

Output:



Example 2: Retrieving total quantities ordered for different products.select Product_ID, sum(Quantity_Ordered) from customer_order

group by Product_ID;

Output:



ORDER BY Clause:

Is used to sort the records in result set either in ascending or descending order .

Syntax:SELECT expressions

FROM tables

WHERE conditions

ORDER BY expression [ ASC | DESC ];



Example: Display full customer names in ascending order.

select Customer_ID, concat(FirstName,' ',LastName) Customer_Name

from customers order by Customer_Name ASC;

Output:



HAVING Clause is used in the SELECT statement to specify filter conditions for group of rows or aggregates.

Example: Retrieving total quantities ordered for different products where total quantities order for each product is less than 100.

select Product_ID, sum(Quantity_Ordered) TotalQuantityoOrdered

from customer_order group by Product_ID having

TotalQuantityoOrdered<100;



Output:



LIKE Clause:

Is used to search for a specified pattern in a column.

Uses % sign to define wildcards (missing letters) both before and after the pattern.

Syntax:SELECT column_name(s)

FROM table_name

WHERE column_name LIKE pattern;



Example 1: Retrieving products those contain the word “Silk” in names.

SELECT Product_ID,Product_name FROM products WHERE

Product_name LIKE '%Silk%';

Output:



Example 2: Retrieving customers whose names start with alphabet w.

SELECT Customer_ID,FirstName FROM customers WHERE

FirstName LIKE 'w%';

Output:


Joins in MySQL

Joins are used to combine the data from two tables, with the result being a new, temporary table.

Joins are performed based on something called a predicate, which specifies the condition to use in order to perform a join.


Joins in MySQL (Contd.)

Join types:

o Outer Join:

• Left Outer Join

• Right Outer Join

o Inner Join

o Self Join



Lets take two tables to understand joins:

Employee Location



Left Outer Join:

Retains all of the rows of the left table, regardless of whether there is a row that matches on the right table.

Example:

SELECT * FROM employee LEFT OUTER JOIN location

ON employee.empID = location.empID;



Output:



Right Outer Join:

Retains all of the rows of the right table, regardless of whether there is a row that matches on the left table.

Example:

SELECT * FROM employee RIGHT OUTER JOIN location

ON employee.empID = location.empID;



Output:



Inner Join:

Returns only the rows that actually match based on the join predicate.

Example:

SELECT * FROM employee INNER JOIN location ON

employee.empID = location.empID;



Output:



Self Join:

Uses a different alias for same table.

Used to compare records within one table.

Treats one table as two separate tables by using alias.



Example: Retrieving names of the customers who stay in the city in which customer named White stays.

SELECT c1.FirstName

FROM customers c1, customers c2

WHERE c1.city = c2.City AND c2.FirstName='White';



Output:


Nested Queries

A MySQL subquery is a query that is nested inside another query, such as SELECT, INSERT, UPDATE or DELETE.

A subquery returns values that are used to execute an outer query. A subquery can return one or more values.

If a subquery returns a single value, you can use comparison operators to compare it with the expression in the WHERE clause.

If a subquery returns multiple values, the following keywords can be used to cater the requirements:

IN or Not IN

EXISTS or NOT EXISTS


Nested Queries (Contd.)

Example 1: Displaying the customer ID, first name, and last name of the customer whose order ID is 1.

SELECT Customer_ID, FirstName, LastName Inner Query

FROM Customers

WHERE Customer_ID= (SELECT Customer_Order.Customer_iD FROM

Customer_Order WHERE Order_ID=1);

Outer Query



Output:



Example 2: Retrieving order ID, product ID, customer ID, price of each product, and total amount for each order.

Select Order_ID, Product_ID, Customer_ID,

(select price from products where

products.product_ID=customer_order.Product_ID)Price,

Quantity_Ordered,

(Quantity_Ordered*(select price from products where

products.product_ID=customer_order.Product_ID)) Amount

from customer_order;



The output of the preceding query will be:



Example 3: Retrieving product name and price records of the products that have an above average price:

SELECT Product_Name, Price FROM ProductsWHERE

Price>(SELECT AVG(Price) FROM Products);



The output of the preceding query will be:


Database Security and Privileges (Contd.)

MySQL ensures security by allowing authorized users to access the database.

MySQL provides various commands to create and delete user accounts.

Creating Users:

The CREATE USER statement is used to create MySQL accounts for users.

Syntax:

CREATE USER user_specification IDENTIFIED BY password;

Example:

CREATE USER'smithj'@'localhost' IDENTIFIED BY 'smith123';



Verify the creation of user accounts using the following query:

SELECT * FROM mysql.user;

Output:



Renaming a user account:

Using the RENAME USER statement.

Syntax:

RENAME USER old_account_name TO new_account_name;

Example:RENAME USER 'smithj'@'localhost' TO

'smith_louise'@'localhost';




Output:



Changing user account password :

Using the SET PASSWORD statement.

Syntax:SET PASSWORD [FOR account_name]=

{

PASSWORD('text_password')

|'encrypted_password'

}

Example:SET PASSWORD FOR 'smith_louise'@'localhost' =PASSWORD('pwd_smith_l_123');




Output:



GRANT Statement:

Grants users various privileges to database objects to ensure security.

Syntax:

GRANT privileges ON object TO user;



Privileges can be of following types:

Privilege Description

SELECTAbility to perform SELECT statements on the table.

INSERTAbility to perform INSERT statements on the table.

UPDATEAbility to perform UPDATE statements on the table.

DELETEAbility to perform DELETE statements on the table.

INDEXAbility to create an index on an existing table.



Privilege Description

CREATEAbility to perform CREATE TABLE statements.

ALTERAbility to perform ALTER TABLE statements to change the table definition.

DROPAbility to perform DROP TABLE statements.

ALLGrants all permissions except GRANT OPTION.



In the syntax, object specifies the name of the database object that you are granting permissions for. It can be a table, a function, or a stored procedure.

In the case of granting privileges on a table, this would be the table name.

User specifies the name of the user who will be granted specified privileges.

Viewing grant information:

SHOW GRANTS statement can be used. T

Syntax:

SHOW GRANTS FOR account_name;



Example 1:

GRANT SELECT, INSERT, UPDATE, DELETE ON hotels_chain.* TO

'smith_louise'@'localhost';

SHOW GRANTS FOR 'smith_louise'@'localhost';

Output:



Example 2:

GRANT ALL ON *.* TO 'smith_louise'@'localhost';

The above example grants all permissions on all databases to the user account, smithj@localhost.


Output:



REVOKE Statement:

Revokes privileges from users to ensure security.

Syntax:

REVOKE privileges ON object FROM user;



Example:

REVOKE ALL ON *.* FROM 'smith_louise'@'localhost';


Output:



Deleting Users:

The DROP USER statement is used to delete MySQL user accounts.

Syntax:

DROP USER user_specification;

Example:

DROP USER 'smith_louise'@'localhost';




Output:



Transaction:

Is a logical unit of work requested by a user to be applied to the database objects.

Groups one or more SQL statements into a single logical unit.

Works on tables that use transaction-safe storage engines, like InnoDB and BDB.

Syntax for creating a transaction:

START TRANSACTION;

Statements

COMMIT|ROLLBACK;



Running the COMMIT command will explicitly end the current transaction. Changes will be committed.

Running the ROLLBACK command will explicitly end the current transaction. Changes will be rolled back.

Example:

START TRANSACTION;

INSERT INTO Products VALUES(11,'Red Soft Carpets',500,300,400,4000);

COMMIT;

select * from products;



Output:



SAVEPOINT Statement:

Sets a named transaction savepoint with a name of identifier. If the current transaction has a savepoint with the same name, the old savepoint is deleted and a new one is set.

Syntax:

SAVEPOINT identifier



ROLLBACK TO SAVEPOINT Statement:

Rolls back a transaction to the named savepoint without terminating the transaction.

Syntax:

ROLLBACK TO [SAVEPOINT] identifier



Example:

START TRANSACTION;

INSERT INTO Customers VALUES(11,'Paul','Symonds','Bin Day -23,4','Texas ',9902345);

INSERT INTO Customer_Order VALUES(14,1,5,5);

SAVEPOINT sav1;

INSERT INTO Customers VALUES(12,'Ren','Dreamer', 'Green Street-97,3','LA', 8802399);

INSERT INTO Customer_Order VALUES(15,10,10,3);

ROLLBACK TO SAVEPOINT sav1;

INSERT INTO Customers VALUES(13,'Jen', 'Dreamer','Green Street-97,3','LA',8802399);

insert into Customer_Order values(16,1,6,3);

COMMIT;


Controlling Transactions

SAVEPOINT B

SAVEPOINT A

DELETE

INSERT

UPDATE

INSERT

COMMITTime

Transaction

ROLLBACK

to SAVEPOINT B

ROLLBACK

to SAVEPOINT A

ROLLBACK


Quiz

1. Which model organizes data in a tree structure?

Ans Hierarchical model


Quiz (Contd.)

2. What does symbol represents in an ER diagram?

Ans Entity


Quiz (Contd.)

3. Which language has statements, such as CRATE, ALTER, DROP, TRUNCATE, COMMENT, and RENAME?

Ans DDL


Quiz (Contd.)

4. Which command removes tables including indexes and privileges and cannot be rolled back?

Ans DROP TABLE Statement


Quiz (Contd.)

5. Which command explicitly ends the current transaction without saving the changes made to the database?

Ans ROLLBACK

Case Study

• Mike is a database programmer. He needs to save the following details about the employees working for an organization in the Employee database:• Employee ID• Employee Name• Employee Category and• Basic Salary

• In addition, Mike also needs to store the names of various departments belonging to the organization in the database while ensuring that every department is identified by using a unique ID. He also needs to ensure that there is minimal data redundancy.

Case Study (Contd.)

• Question 1• How can Mike ensure that he creates the required table/s inside the

Employee database only?

Case Study (Contd.)

• Solution 1:• Before writing any Create Table statement, Mike should activate the

Employee database by using the use statement.

• Use employee;

Case Study (Contd.)

• Question 2• Mike has decided to create the Emp_Details table with the following fields to store

the employee details:• Dept_No int• Dept_Name varchar• Emp_ID int• Emp_Name varchar• Emp_Category varchar• Basic_Sal int

• The Basic_Sal depends on the Emp_Category, which has only I, II, or III as its allowed values. The Basic_Sal for employees of category, I, II, and III is 25000, 18000, and 12000, respectively.

• Analyse the preceding scenario and determine if the table structure proposed by Mike is appropriate or not. If not, suggest reasons for the same and the technique that should be implemented to resolve the problems with the table.

Case Study (Contd.)

• Solution 2• The table structure is not appropriate. The table is not normalized which will

result in redundancy of data. For example, if there are 10 employees working in the Sales department, for every record inserted in the table, Dept_No and Dept_Name will be inserted again and again.

Case Study (Contd.)

• Question 3• Consider the preceding Emp_Details table. Identify the primary key in the

table. Write the SQL statement that Mike should use to create the table and also define the primary key in the table.

Case Study (Contd.)

• Solution 3• Mike should create a composite primary key on the columns, Dept_No and

Emp_ID

• Create table Emp_Details(Dept_No int, Dept_Namevarchar(20),Emp_ID int, Emp_Name varchar(30),Emp_Categoryvarchar(5),Basic_Sal int, primary key(Dept_No , Emp_ID)

Case Study (Contd.)

• Question 4• Analyse the Emp_Details table and identify its current normal form. Also

provide the reason for the same.

Case Study (Contd.)

• Solution 4• The table is in 1NF, because all the non key attributes do not depend on the

entire primary key. If Dept_No and Emp_ID make up the primary key in the table, all the remaining fields should depend on the entire primary key. But Dept_Name depends only on Dept_No, which is a part of the primary key , thus table is not in 2NF.

Case Study (Contd.)

• Question 5• To attain normalization, Mike has decided to split the Emp_Details table into

the following tables:• Emp_Department (Dept_No, Emp_ID)

• Employee (Emp_ID, Emp_Name, Emp_Category)

• Department (Dept_No, Dept_Name)

• Wages(Emp_Category, Basic_Sal)

• Identify the primary keys in all the preceding tables. Write the SQL statements for creating the preceding tables and define the primary keys in all the tables.

Case Study (Contd.)

• Solution 5• create table emp_department(Dept_No int, Emp_ID int, primary

key(D_No,E_ID);

• create table employee(Emp_ID int primary key,

• Emp_Name varchar(20),Emp_Category varchar(5));

• create table department(Dept_No int primary key,Dept_Name varchar(30));

• create table Wages(Emp_Category varchar(4) primary key,Basic_Sal int);

Case Study (Contd.)

• Question 6• Mike needs to define a relationship between the Employee table and Wages

table. Identify the field on the basis of which this relationship can be defined. In addition, identify the parent and the child table in the relationship. Write the SQL statement to create the relationship between these tables.

Case Study (Contd.)

• Solution• A relationship can be defined between the tables by using a foreign key. This

relationship can be defined between the tables on the basis of the common column, Emp_Category. Wages is the parent table and Employee is the child table.

• create table employee(Emp_ID int primary key,

• Emp_Name varchar(20),Emp_Category varchar(5),

• Foreign key(Emp_Category) references Wages(Emp_Category))Engine=InnoDB;

Case Study (Contd.)

• Question 7• Write the SQL statements to insert the records in the Wages table as specified

in the preceding scenario.

Case Study (Contd.)

• Solution• insert into Wages values('I',25000),('II',18000),('III',12000);

Case Study (Contd.)

• Question 8• The Employee table contains the following records inside it:

• Write the SQL statement to update the Emp_Category of Vanya to I.

Emp_ID Emp_Name Emp_Categor

y

101 Sam I

102 Peter I

89 Sammy III

78 Vanya II

Case Study (Contd.)

• Solution 8• Update Employee set Emp_cateory=’I’ where Emp_ID=78;

Case Study (Contd.)

• Question 9• Mike needs to retrieve and display the Emp_ID, Emp_Name, Emp_Category,

and Wages of all the employees. Write the SQL statement that he needs to use for the same.

Case Study (Contd.)

• Solution 9• select Emp_ID, Emp_Name, Employee.Emp_Category, Basic_Sal from

Employee Join Wages

on Employee.Emp_Category=Wages.Emp_Category;

Case Study (Contd.)

• Question 10• Write the SQL statement to remove the record for Employee with ID 78 from

the Employee table.

Case Study (Contd.)

• Solution 10• Delete from Employee where Emp_ID=78;


Summary

In the session learned that:

Database models defines the logical structure of a database is modeled.

Some of the types of Database Models are:

Hierarchical model

Network model

Relational model

Object-oriented model


Summary (Contd.)

RDBMS is a database management system represents data in terms of tuples(rows) and is used to manage relational databases.

Database normalization is to restructure the logical data model of a database to:

Eliminate redundancy

Organize data efficiently

Reduce the potential for data anomalies

ER Diagrams represent conceptual level of a database system.


Summary (Contd.)

MySQL uses many different data types broken into three categories:

Numeric

Date and time

String

CREATE TABLE statement is used to create tables.

ALTER TABLE statement changes the structure of an existing table.

DROP TABLE statement removes one or more tables including indexes and privileges.


Summary (Contd.)

INSERT statement inserts records into a table.

UPDATE statement can update one or more field altogether.

DELETE FROM statement deletes records from a table.

SELECT statement can fetch records from a one or more tables at a time.

Joins are used to combine the data from two tables, with the result being a new, temporary table.

The CREATE USER statement is used to create MySQL accounts for users.


Summary (Contd.)

The DROP USER statement is used to delete MySQL user accounts.

GRANT Statement grants users various privileges to database objects to ensure security.

REVOKE Statement revokes privileges from users to ensure security.

Transaction is a logical unit of work requested by a user to be applied to the database objects.

Technology

RDBMS with MySQL