Sql wksht-2

SQL Simple Queries – Ch 5

SQL Queries - Basics
Worksheet - 2
DATABASE OPERATIONS
1 CREATE Database Statement:
This statement is used to create a database.

Syntax

CREATE DATABASE { databasename }

Arguments database
Is the name of the database which is to be created..

Example:
CREATE DATABASE student

2 Deleting a database with DROP statement
This statement is used to delete a database.

Syntax

DROP DATABASE { databasename }

Arguments: database
Example:

DROP DATABASE student

TABLE OPERATIONS
3 Creating a Table – the CREATE TABLE statement
CREATE TABLE tablename (Column1, Column2, Column3,…)

Each column is created as
ColumnName DataType Options

Example:
CREATE TABLE Student
(
RollNo nvarchar(32),
DOB DATE,
FullName nvarchar(50),
Address NVARCHAR(120),
City NvarChar(40),
State NVarChar(50),
PostalCode nvarchar(20),
HomePhone nvarchar(20),
);

Prof. Mukesh N. Tekwani Page 1 of 11


4 Delete a table with DROP TABLE statement
DROP TABLE TableName

COLUMN OPERATIONS
5 How will you specify unique values in a column?

You may want a column to receive a unique value for each of its records. To specify
that a column will require unique values, use the UNIQUE keyword.

USE College;

CREATE TABLE Students
(
RollNo int UNIQUE,
FirstName nvarchar(50),
LastName nvarchar(50) NOT NULL
);

When a column has been marked as unique, during data entry, the user must provide
a unique value for each new record created. If an existing value is assigned to the
column, this would produce an error:

USE College;

CREATE TABLE Students
(
StudentNumber int UNIQUE,
LastName nvarchar(50) NOT NULL
);

INSERT INTO Students
VALUES(2, 'Jitesh', 'Patel'),
(9, 'Rani', 'Shah'),
(4, 'Preeti', 'Patel'),
(9, 'Deepak', 'Tiwari'),
(6, 'Priyanka', 'Chopra');

By the time the fourth record is entered, since it uses a student number that exists already,
the database engine would produce an error.

6 What is a check constraint? Explain, with the help of a suitable example, how to
create a check constraint.
Check Constraint:
When performing data entry, in some columns, we may want to restrict a range of
values that are allowed. We can create a rule that must be followed on a combination
of columns before the record can be created. For example, you can ask the database
engine to check that at least one of two columns received a value. For example, on a
table that holds information about customers, you can ask the database engine to
check that, for each record, either the phone number or the email address of the

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customer is entered.

The ability to verify that one or more rules are respected on a table is called a check
constraint. A check constraint is a Boolean operation performed by the SQL
interpreter. The interpreter examines a value that has just been provided for a
column.

If the value is appropriate:

a. The constraint produces TRUE
b. The value gets accepted
c. The value is assigned to the column

If the value is not appropriate:

a. The constraint produces FALSE
b. The value gets rejected
c. The value is not assigned to the column

You create a check constraint at the time you are creating a table.

Example:

1. To create a table that has a check mechanism, type the following:

CREATE TABLE Customers
(
CustomerID int ,
AccountNumber nchar(10) UNIQUE,
FullName nvarchar(50) NOT NULL,
PhoneNumber nvarchar(20),
EmailAddress nvarchar(50),

CONSTRAINT CK_CustomerContact
CHECK ((PhoneNumber IS NOT NULL) OR (EmailAddress IS NOT NULL))
);
2. To add records to the new table, type the following:

INSERT INTO Customers(AccountNumber, FullName,
PhoneNumber, EmailAddress)
VALUES('39', 'Anita', '301-128-3506', 'anita@yahoo.com'),
('62', 'Preeti', '(202) 050-1629', 'preeti@hotmail.com'),
('86', 'Julie', '410-114-6820', 'julie@email.net');
3. To try adding a new record to the table, type the following:

INSERT INTO Customers(AccountNumber, FullName)
VALUES('22', 'Jiten')

Notice that you receive an error.

7 Explain how a default value can be given to a column.

A default value is one that a column would apply to its record if a value is not



provided. You can assign a default value when creating a table.

To specify the default value in a SQL statement, when creating the column, before the
semi-colon or the closing parenthesis of the last column, assign the desired value to
the DEFAULT keyword.

After creating the table, the user does not have to provide a value for a column that
has a default. If the user does not provide the value, the default would be used when
the record is saved.

Example 1:

CREATE TABLE Employees
(
FullName NVARCHAR(50),
Address NVARCHAR(80),
City NVARCHAR(40),
State NVARCHAR(40) DEFAULT 'Maharashtra',
PinCode NVARCHAR(4) DEFAULT '400001',
Country NVARCHAR(20) DEFAULT 'India'
);

Example 2:

The default value can also come from a function.

(
EmployeeName nvarchar(50),
DateHired datetime DEFAULT GETDATE(),
Address nvarchar(50),
City nvarchar(40),
State nchar(2) DEFAULT 'Maharashtra',
PostalCode NVARCHAR(4),
Country NVARCHAR(20)
);

Example 3:

If the table exists already and you want to add a column that has a default value, use
this method:

ALTER TABLE TableName ADD ColumnName Options

Here is an example:

USE Exercise1;

ALTER TABLE Employees
ADD HomePhone nvarchar(20) default '(000) 000-0000';

8 Explain how a column can contain an expression.
An expression used on a column is a combination of operators and operands used to
produce the value of the column. The user will not enter a value for such a column.


Example 1:
To create an expression in SQL, in the placeholder of the column, enter the name of
the column, followed by AS, and followed by the desired expression.

CREATE TABLE Circle
(
CircleID int NOT NULL,
Radius decimal(8, 3) NOT NULL,
Area AS Radius * Radius * PI()
);

When performing data entry, we must not provide a value for a column that has an
expression; the SQL interpreter would provide the value automatically.

INSERT INTO Circle(Radius) VALUES(46.82);

RECORD OPERATIONS
9 Updating a Record
Updating a record means changing or more of its values. SQL provides the UPDATE
keyword:

Example 1:
UPDATE TableName
SET ColumnName = Expression

Example 2:
UPDATE TableName
SET ColumnName = Expression
WHERE Condition(s)

Example 3:
UPDATE Videos
SET YearReleased = 1996
WHERE VideoID = 5;

10 How can a column or a table be renamed?
The sp_rename command changes the name of an object.

Syntax

sp_rename 'object_name' , 'new_name' , 'object_type'

‘objecttype’ is the type of the object being renamed. This object may be a TABLE, a
COLUMN, a DATABASE, or an INDEX.

To change the name of a column, we specify the command as shown below:



Example 1:

This example renames the contact title column in the customers table to title.

EXEC sp_rename 'customers.[contact title]', 'title', 'COLUMN'

Example 2:
To rename a column called rno to RollNo in the tybsc table:
EXEC sp_rename 'tybsc.rno', 'RollNo', 'COLUMN'

To change the name of a table, we specify the command as shown below:
EXEC sp_rename 'tybscit', 'tybsc'

11 How can a database be deleted?
The DROP DATABASE command is used to delete or DROP a database.

Syntax
DROP DATABASE database_name [ ,...n ]

One or more databases can be deleted in this way.

To use DROP DATABASE, the database context of the connection must be in the master
database. A database that is currently in use cannot be dropped.

Example 1:

Drop a single database called publishing,

DROP DATABASE publishing

Example 2:

Delete databases called sybscit and tybscit.

DROP DATABASE sybscit, tybscit

12 Explain functions in SQL.

In Transact-SQL, the primary formula of creating a function is:

CREATE FUNCTION FunctionName()

For a function to be useful, it must produce a result and return a value. When creating
a function, we must specify the type of value that the function would return.

To provide this information, after the name of the function, type the RETURNS
keyword followed by a definition for a data type.


Example 1:

CREATE FUNCTION Addition()
RETURNS Decimal(6,3)

After specifying the type of value that the function would return, you can create a
body for the function. The body of a function starts with the BEGIN and ends with the
END keywords.

BEGIN

END

Between the BEGIN and END keywords, we can define the statements the function must
perform. After performing this assignment, just before the END keyword, you must specify
the value that the function returns. This is done by typing the RETURN keyword followed
by an expression.

BEGIN
RETURN Expression
END

Function Calling:
After a function has been created, we can use the value it returns. Using a function is
also referred to as calling it. To call a function, you must qualify its name. To do this,
type the name of the database in which it was created, followed by the period
operator, followed by dbo, followed by the period operator, followed by the name of
the function, and its parentheses. The formula to use is:

DatabaseName.dbo.FunctionName()

A Parameterized Function
To create a function that takes a parameter, specify a name and the type of value of
the parameter(s) in its parentheses. Here is an example:

CREATE FUNCTION Addition(@Number1 Decimal(6,2))

When a function takes a parameter, in the body of the function, you can use the
parameter as if you knew its value, as long as you respect the type of that value. Here
is an example:

CREATE FUNCTION Addition(@Number1 Decimal(6,2))
BEGIN
RETURN @Number1 + 1450
END



13 Explain what is meant by a procedure in SQL.
A procedure is a collection of SQL statements.
One of the simplest procedures is selecting columns from a table. This is done with the
SELECT operator.

For example, to create a stored procedure that would hold a list of students from a
table named Students, we would create the procedure as follows:

CREATE PROCEDURE GetStudDetails
AS
BEGIN
SELECT FirstName, LastName, DateOfBirth, Gender
FROM Students
END

Executing a Procedure
To execute a procedure, you use the EXECUTE keyword followed by the name of the
procedure.

EXECUTE ProcedureName

Instead of EXECUTE, you can use the EXEC keyword:

EXEC ProcedureName

For example, if you have a procedure named GetStudDetails, to execute it, we would
type:

EXECUTE GetStudentIdentification

Example 3:
Write a procedure that creates the full name using the fields ‘FirstName’ and ‘LastName’
CREATE PROCEDURE GetStudentIdentification
AS
BEGIN
SELECT FullName = FirstName + ' ' + LastName,
DateOfBirth, Gender
FROM Students
END

Example 4:
Write a procedure that calls a function in its body.
USE STUDENT;

CREATE PROCEDURE GetStudentsAges
AS
BEGIN
SELECT FullName = FirstName + N' ' + LastName,
DATEDIFF(year, DateOfBirth, GETDATE()) AS Age,
Gender
FROM Students
END



14 How can a procedure be modified?
ALTER PROCEDURE ProcedureName
AS
Body of Procedure

How can a procedure be deleted?

When we don’t need a procedure anymore, we can delete it.

There are various types of stored procedures, some of which are considered
temporary. Those types of procedures delete themselves when not needed anymore,
such as when the person who created the stored procedure disconnects from the
database or shuts down the computer. Otherwise, to delete a procedure, you can use
either the Object Explorer or SQL.

To delete a procedure in SQL, the syntax to use is:

DROP PROCEDURE ProcedureName

INDEX
15
What is an index?

If you take a look at the last pages of a book (such as a book about mathematics,
computer science, etc), you may find a series of pages that start in a section label
Index. The words in that series allow you to locate a section of the book that
mentions, explains, or describes the word and related topics. An index in a book
makes it easy and fast to get to a section of a book that deals with a particular topic.

Like a book, a table or a view can use the mechanism provided by an index. In a table
or a view, an index is a column (or many columns) that can be used to locate records
and take a specific action based on some rule reinforced on that (those) column(s).

16
How can an index be created in SQL?

To create an index in SQL, the basic formula to follow is:

CREATE INDEX IndexName ON Table/View(Column(s))

The creation on an index starts with the CREATE INDEX expression, followed by a
name for the index, followed by the ON keyword. In the Table/View placeholder, enter
the name of the table or view for which you want to create the index, followed by
parentheses in which you enter at least one column.

Example 1:

-- =============================================
-- Database: Exercise
-- =============================================
USE master


-- Drop the database if it already exists

IF EXISTS (
SELECT name
FROM sys.databases
WHERE name = 'Exercise'
)
DROP DATABASE Exercise

CREATE DATABASE Exercise

USE Exercise;

-- =============================================
-- Database: Exercise
-- Table; Employees
-- =============================================
(
EmployeeNumber int NOT NULL,
LastName nvarchar(20) NOT NULL,
Username nchar(8) NOT NULL,
DateHired date NULL,
HourlySalary money
);
GO

INSERT INTO Employees
VALUES(62480, 'James', 'Haans', 'jhaans', '1998-10-25', 28.02),
(35844, 'Gertrude', 'Monay', 'gmonay', '2006-06-22', 14.36),
(24904, 'Philomène', 'Guillon', 'pguillon', '2001-10-16', 18.05),
(48049, 'Eddie', 'Monsoon', 'emonsoon', '08/10/2009', 26.22),
(25805, 'Peter', 'Mukoko', 'pmukoko', '03-10-2004', 22.48),
(58405, 'Chritian', 'Allen', 'callen', '06/16/1995', 16.45);
GO

CREATE INDEX IX_Employees
ON Employees(EmployeeNumber);
GO

If the index will include more than one column, list them separated by commas. Here
is an example:

CREATE INDEX IX_Employees
ON Employees(LastName, Username);
GO

17
How can an index be deleted?

If you don't need an index anymore, you can delete it.

The basic syntax to delete an index is:

DROP INDEX IndexName ON TableName;



In this formula, replace the TableName with the name of the table that contains the
index. Replace the IndexName with the name of the index you want to get rid of.

Here is an example:

USE Exercise;
GO
DROP INDEX IX_Employees ON Employees;

TRIGGERS
18
What is a trigger?

When an action has been performed on a table, such as adding a new record, changing
(editing/updating) an existing record, or deleting a record, the table produces a
notification. We say that the table fires an event. You can use this occurring event to
take some action.

A trigger is an action that is performed behind-the-scenes when an event occurs on a
table.


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