Zia - Lecture - 24-April-2014.pdf

7/25/2019 Zia - Lecture - 24-April-2014.pdf

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DBMS

Lectures


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Contents

Create Database

Create Table

Alter Table Create Constraints

Create index


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Create Database

The CREATE DATABASE statement is used to

create a database.

SQL CREATE DATABASE Syntax

Example

CREATE DATABASE dbname;

CREATE DATABASE student_db;


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Create Table

The CREATE TABLE statement is used to create

a table in a database.

Tables are organized into rows and columns;

and each table must have a name.


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Create Table

SQL CREATE TABLE Syntax

CREATE TABLE table_name

(column_name1 data_type(size),

column_name2 data_type(size),

column_name3 data_type(size),....

);


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Create Table

Example

CREATE TABLE Persons

(PersonID int,

LastName varchar(255),

FirstName varchar(255),

Address varchar(255),

City varchar(255)

);


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Alter Table

The ALTER TABLE statement is used to:

Add

Delete

Modify

the columns in an existing table.


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Alter Table

To add a column in a table, use the following

syntax:

Example:

ALTER TABLE table_nameADD column_name datatype

ALTER TABLE Persons

ADD DateOfBirth date


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Alter Table

To delete a column in a table, use the

following syntax:

Example:

ALTER TABLE table_nameDROP COLUMN column_name

ALTER TABLE Persons

DROP COLUMN DateOfBirth


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Alter Table

To modify the data type of a column in a table,

use the following syntax:

Example:

ALTER TABLE table_nameMODIFY column_name datatype

ALTER TABLE Persons

MODIFY DateOfBirth varchar(255)


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Alter Table

Change/modify SQL Server / MS Access:

My SQL / Oracle:

Oracle 10G and later:

ALTER TABLE table_name

ALTER COLUMN column_name datatype


MODIFY COLUMN column_name datatype


MODIFY column_name datatype


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SQL Constraints

SQL constraints are used to specify rules forthe data in a table.

If there is any violation between the

constraint and the data action, the action isaborted by the constraint.

Constraints can be specified when the table is

created (inside the CREATE TABLE statement)or after the table is created (inside the ALTERTABLE statement).


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SQL Constraints

NOT NULL

UNIQUE

PRIMARY KEY FOREIGN KEY

CHECK

DEFAULT


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SQL Constraints

SQL CREATE TABLE + CONSTRAINT Syntax

CREATE TABLE table_name(

column_name1 data_type(size) constraint_name,

column_name2 data_type(size) constraint_name,

column_name3 data_type(size) constraint_name,....

);


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NOT NULL - Constraint

NOT NULL - Indicates that a column cannot

store NULL value

The NOT NULL constraint enforces a field to

always contain a value.

This means that you cannot insert a new

record, or update a record without adding a

value to this field.


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NOT NULL - Constraint

Example

CREATE TABLE PersonsNotNull

(P_Id int NOT NULL,

LastName varchar(255) NOT NULL,



City varchar(255)

)


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UNIQUE - Constraints

UNIQUE - Ensures that each row for a column

must have a unique value

OR

The UNIQUE constraint uniquely identifies

each record in a database table.

Note: You can have many UNIQUE constraints

per table


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Example


(

P_Id int NOT NULL UNIQUE,



Address varchar(255),City varchar(255)

)


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Example


(P_Id int NOT NULL,



Address varchar(255),City varchar(255),

CONSTRAINT uc_PersonID UNIQUE (P_Id,LastName)

)


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UNIQUE Constraints Alter Table

To create a UNIQUE constraint on the "P_Id"

column when the table is already created, use

the following SQL:

ALTER TABLE Persons

ADD UNIQUE (P_Id)

ALTER TABLE Persons

ADD CONSTRAINT uc_PersonID UNIQUE (P_Id,LastName)


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UNIQUE Constraints Alter Table

To drop a UNIQUE constraint, use the

following SQL:

ALTER TABLE Persons

DROP CONSTRAINT uc_PersonID


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PRIMARY KEY - Constraints

PRIMARY KEY - A combination of a NOT NULL

and UNIQUE.

Ensures that a column (or combination of two

or more columns) have an unique identity

which helps to find a particular record in a

table more easily and quickly

Each table should have a primary key, and

each table can have only ONE primary key.


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Example


(

P_Id int NOT NULL PRIMARY KEY,




)


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Example


(

P_Id int NOT NULL,LastName varchar(255) NOT NULL,



City varchar(255),CONSTRAINT pk_PersonID PRIMARY KEY (P_Id,LastName)

)


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PK Constraints Alter Table

To create a PRIMARY KEY constraint on the

"P_Id" column when the table is already

created, use the following SQL:

ALTER TABLE Persons

ADD PRIMARY KEY (P_Id)

ALTER TABLE Persons

ADD CONSTRAINT pk_PersonID PRIMARY KEY (P_Id,LastName)


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PK Constraints Alter Table

To drop a PRIMARY KEY constraint, use the

following SQL:

ALTER TABLE Persons

DROP CONSTRAINT pk_PersonID


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FOREIGN KEY - Constraints

FOREIGN KEY - Ensure the referential integrity

of the data in one table to match values in

another table

A FOREIGN KEY in one table points to a

PRIMARY KEY in another table.


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Example

CREATE TABLE Orders

(

O_Id int NOT NULL PRIMARY KEY,

OrderNo int NOT NULL,

P_Id int FOREIGN KEY REFERENCES Persons(P_Id)

)

P_Id LastName FirstName

1 Ali Muhammad

2 Khan Ahmad

3 Aslam Muhammad

O_Id OrderNum P_Id

1 456 2

2 457 3

3 458 1

Persons Orders


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ExampleCREATE TABLE Orders

(

O_Id int NOT NULL,


P_Id int,

PRIMARY KEY (O_Id),

CONSTRAINT fk_PerOrders FOREIGN KEY (P_Id)

REFERENCES Persons(P_Id)

)

P_Id LastName FirstName

1 Ali Muhammad

2 Khan Ahmad

3 Aslam Muhammad

O_Id OrderNum P_Id

1 456 2

2 457 3

3 458 1

Persons Orders


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FK Constraints Alter Table

To create a FOREIGN KEY constraint on the

"P_Id" column when the "Orders" table is

already created, use the following SQL:

ALTER TABLE Orders

ADD FOREIGN KEY (P_Id)


ALTER TABLE OrdersADD CONSTRAINT fk_PerOrders

FOREIGN KEY (P_Id) //multiple columns can be added



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FK Constraints Alter Table

To drop a FOREIGN KEY constraint, use the

following SQL:

ALTER TABLE Orders

DROP CONSTRAINT fk_PerOrders


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CHECK - Constraints

CHECK - Ensures that the value in a column

meets a specific condition

If you define a CHECK constraint on a single

column it allows only certain values for this

column.

If you define a CHECK constraint on a table it

can limit the values in certain columns based

on values in other columns in the row.


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CHECK - Constraints

Example:


(P_Id int NOT NULL CHECK (P_Id>0),




)


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CHECK Constraints Alter Table

To create a CHECK constraint on the "P_Id"


the following SQL:

ALTER TABLE Persons

ADD CHECK (P_Id>0)

ALTER TABLE Persons

ADD CONSTRAINT chk_Person CHECK (P_Id>0 AND

City=Islamabad')


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CHECK Constraints Alter Table

To drop a CHECK constraint, use the following

SQL:

ALTER TABLE Persons

DROP CONSTRAINT chk_Person


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DEFAULT - Constraints

DEFAULT - Specifies a default value when

specified none for this column


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Example:


(P_Id int NOT NULL,



Address varchar(255),City varchar(255) DEFAULT ISLAMABAD '

)


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Example:

CREATE TABLE Orders

(O_Id int NOT NULL,


P_Id int,

OrderDate date DEFAULT GETDATE()

)


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DEFAULT Constraints Alter Table

To create a DEFAULT constraint on the "City"


the following SQL:

ALTER TABLE Persons

MODIFY City DEFAULT ISLAMABAD'


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DEFAULT Constraints Alter Table

To drop a DEFAULT constraint, use the

following SQL:

ALTER TABLE Persons

ALTER COLUMN City DROP DEFAULT


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Create index


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Create index

An index can be created in a table to find data

more quickly and efficiently.

The CREATE INDEX statement is used to create

indexes in tables.


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Create index

SQL CREATE INDEX Syntax

Creates an index on a table. Duplicate valuesare allowed:

CREATE INDEX index_name

ON table_name (column_name)


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Create index

Example

CREATE INDEX PIndex

ON Persons (LastName)

CREATE INDEX PIndex

ON Persons (LastName, FirstName)


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Class Activity

Make group of 3 people

Normalize the date up to 3NF

Time 30min


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Solution

EMPLOYEE

DEPARTMENT

DEPT_LOCATION

WORKS_ON

PROJECT


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Class Activity

ENAME,

NIC,

DOB,

ADDRESS,

DEPTLOC,

DEPTNAME,

DEPTNUM,

DEPTTYPE,

PROJNAME,

PROJNUM,

PROJLOC,

WORKHOUR


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DEPTTYPE

NIC

NIC

DOB

Documents

Zia - Lecture - 24-April-2014.pdf