Sql xp 08

Implementing Views and Batches

Objectives
In this lesson, you will learn to:
Create, alter, drop, and rename views
Update data using views
Declare variables
Print messages
Use comments
Use conditional statements
Use the iteration statements

SQL/Lesson 8/Slide 1 of 50
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Getting Started
Views
A view is a virtual table, which gives access to a subset
of columns from one or more tables
Views ensure security of data by restricting access to:
® Specific rows of a table
® Specific columns of a table
® Specific rows and columns of a table
® The rows fetched using joins

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Getting Started (Contd.)
® The statistical summary of data in a given table
® Subsets of another view or a subset of views and tables
Views provide several advantages:
Providing relevant data for users
Hiding data complexity
Organize data from heterogeneous sources
Reducing the object size

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8.D.1 Creating Views
You need to view skills of various employees. Some of the
queries to be executed are as follows:

SELECT vFirstName, vSkill FROM Employee JOIN
PositionSkill ON Employee.cCurrentPosition =
PositionSkill.cPositionCode JOIN Skill ON
PositionSkill.cSkillCode = Skill.cSkillCode
SELECT vFirstName, vLastName,vSkill FROM
Employee JOIN PositionSkill ON
Employee.cCurrentPosition=PositionSkill.cPos
itionCode

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8.D.1 Creating Views (Contd.)
JOIN Skill ON PositionSkill.cSkillCode =
Skill.cSkillCode
SELECT vFirstName, vLastName, vSkill FROM
Employee JOIN PositionSkill
ON Employee.cCurrentPosition
=PositionSkill.cPositionCode
JOIN Skill ON PositionSkill.cSkillCode
=Skill.cSkillCode
AND vFirstName = 'Angela'

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8.D.1 Creating Views (Contd.)
SELECT vFirstName, vLastName,
vQualification, vSkill
FROM Employee JOIN PositionSkill
ON Employee.cCurrentPosition =
PositionSkill.cPositionCode JOIN Skill
ON PositionSkill.cSkillCode =
Skill.cSkillCode
Simplify the task of executing these queries.

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Task List
Identify how to simplify queries
Draft the query for the view
Create the view
Verify that the queries have been simplified by executing the
required queries on the view

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Identify how to simplify queries
Result:
Simplification of the query can be done using views

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Draft the query for the view
Action:
The tables from where the view derives its data are
Employee, positionSkill, and Skill
The columns that are to be included in the view are
vFirstName, vLastName, and vQualification from the
Employee table and vSkill from the Skill table

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Create the view
A view can be created using the CREATE VIEW statement
Syntax
CREATE VIEW view_name
[(column_name [, column_name]...)]
[WITH ENCRYPTION]
AS select_statement [WITH CHECK OPTION]

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Create the view (Contd.)
Action:
In the Query Analyzer window, type:
CREATE VIEW vwEmpSkill
AS
SELECT vFirstName, vLastName,
vQualification, vSkill
FROM Employee JOIN PositionSkill
ON Employee.cCurrentPosition =
PositionSkill.cPositionCode
JOIN Skill
ON PositionSkill.cSkillCode =
Skill.cSkillCode
Press F5 to execute the command
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Verify that the queries have been simplified by
executing the required queries on the view
Action:
SELECT vFirstName, vSkill FROM vwEmpSkill
Press F5 to execute the query
SELECT vFirstName, vLastName, vSkill
FROM vwEmpSkill
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Verify that the queries have been simplified by
executing the required queries on the view (Contd.)
SELECT vFirstName,vLastName,vSkill
FROM vwEmpSkill WHERE vFirstName =
'Angela'
SELECT * FROM vwEmpSkill

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Just a Minute...
Some queries to be executed are as follows:
SELECT vFirstName, vDepartmentName
FROM Employee JOIN Department
ON Employee.cDepartmentCode =
Department.cDepartmentCode

SELECT vFirstName, cDesignation,
vDepartmentName
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Just a Minute (Contd.)
SELECT vFirstName, vAddress, cCity, cZip,
cDesignation, vDepartmentName, vDepartmentHead
WHERE cCity = 'Columbus'
Simplify the task of executing these queries.

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Altering, Dropping, and Renaming Views
Altering Views
You can modify a view by using the ALTER VIEW statement
Syntax
ALTER VIEW view_name [(column_name)]
[WITH ENCRYPTION]
AS select_statement
[WITH CHECK OPTION]

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Altering, Dropping, and Renaming Views (Contd.)
Dropping Views
You can drop a view from a database by using the DROP
VIEW statement
Syntax
DROP VIEW view_name

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Altering, Dropping, and Renaming Views (Contd.)
Renaming Views
A view can be renamed using the sp_rename system stored
procedure
Syntax
sp_rename old_viewname, new_viewname

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8.D.2 Modifying Data Using Views
A view is defined as follows:
CREATE VIEW vwEmployeeCandidate
AS
SELECT Employee.cCandidateCode, vFirstName,
vLastName, cPhone, siTestScore
FROM Employee JOIN InternalCandidate
ON
Employee.cCandidateCode=InternalCandidate.
cCandidateCode

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8.D.2 Modifying Data Using Views (Contd.)
While updating the test score and the telephone number of an
employee, whose candidate code is ‘000018’, the following
command gives an error:
UPDATE vwEmployeeCandidate
SET cPhone = '(614)324-5634', siTestScore=75
WHERE cCandidateCode=‘000018’
Identify the error and correct it so that data in the tables is
modified.

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Task List
Identify the error and a method to modify data
Draft separate statements to update tables
Update tables
Verify that the tables have been updated

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Identify the error and a method to modify data
Modifying data through views
Data is present in the base tables, which can be modified
by modifying data in the view
There are certain restrictions at the time of inserting,
updating, or deleting data through views. These are:
You cannot modify data in a view if the modification
affects more than one underlying table
You cannot change a column that is the result of a
calculation

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Identify the error and a method to modify data (Contd.)
Result:
You are unable to update the attributes because views
allow only one of the underlying tables to be updated at a
time. You need to update the attributes by giving two
separate UPDATE commands

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Draft separate statements to update tables
Action:
The following statement would update the cPhone
attribute in the Employee base table:
UPDATE vwEmployeeCandidate SET cPhone =
'(614)324-5634'WHERE cCandidateCode =
'000018'
The following statement would update siTestScore
attribute in the InternalCandidate table:
SET siTestScore=75
WHERE cCandidateCode='000018'

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Update tables
Action:
SET cPhone = '(614)324-5634'
WHERE cCandidateCode = '000018'

SET siTestScore = 75
Press F5 to execute the statement

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Verify that the tables have been updated
Action:
SELECT * FROM Employee

SELECT * FROM InternalCandidate
Press F5 key to execute the queries

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8.P.1 Modifying Data Using Views
A view was defined as follows:
CREATE VIEW vwNewspaperNewsad
AS
SELECT cNewspaperName,vCity,cZip,dAdStartDate
FROM Newspaper JOIN NewsAd
ON Newspaper.cNewspaperCode =
NewsAd.cNewspaperCode
The following statement, when given to update the table, did
not update the table:
UPDATE cNewspaperNewsAd
SET cZip='88993-4532',dAdStartDate='01/09/99'
WHERE cNewspaperName='Daily News'
Modify data in the base tables.
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Programming for SQL Server
There are several methods of programming SQL Server
applications. The following sections describe the different
approaches that you can use for programming in terms of:
Batches
Variables
Printing Messages
Comments
Control-of-flow statements

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Programming for SQL Server (Contd.)
Batches
Batches are groups of SQL statements submitted together
to SQL Server for execution
SQL server processes a batch interactively or from a file
Variables
You can use a variable to store a temporary value
Syntax
DECLARE @variable_name data_type
Example
DECLARE @Charge int
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In Transact SQL, there are two kinds of variables, local and
global
The variable @Charge is declared within a batch and is lost
when the execution of the batch is over. Such variables are
called local variables and, since we defined them, they are
called the user-defined variables
Global variables are those that are declared by the server
and typically assigned values by the server

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Printing Messages
The PRINT statement is used to display a user-defined
message or the content of a variable on the screen
Example
DECLARE @MyName char (50)
SELECT @MyName = 'Coomar Chris'
PRINT @MyName

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Comment Entry
A comment entry is used in batches to write a description
of the code
It can be written in two ways:
® Multiple line comment entries enclosed within /* and */
® Single line comment entry starting with a -- (double
hyphens)

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Control-of-Flow Language
The control-of-flow language controls the flow of execution
of SQL statements in batches, stored procedures, triggers
and transactions
The control-of-flow statements provided by SQL Server for
programming are:
® The IF…ELSE statement
® The CASE statement
®The WHILE statement

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Just a Minute...
Fill in the blanks:
a. A group of SQL statements submitted together to SQL
server for execution is called a ________.
b. _________ declared within a batch and is lost when the
execution of the batch is over.

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8.D.3 Using the IF Statement
The minimum test score for an internal candidate to be
called for an interview is 80. Write a batch that would display
“Called for interview” along with the test score, if the test
score is more than 80, and display “Rejected - Not called for
interview” if it is less than 80, for an employee whose
employee code is 000008.

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Task List
Identify how to display the required messages
Draft the batch on paper
Execute the batch
Verify the batch

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Identify how to display the required messages
The IF…ELSE Statement
This statement can be used for conditional execution of
SQL statements
Syntax
IF boolean_expression
{sql_statement | statement_block}
[ELSE boolean_expression
{sql_statement | statement_block}]

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Identify how to display the required messages (Contd.)
BEGIN…END Statement
If there are multiple T-SQL statements, then these must
be enclosed within the BEGIN and END keywords
Syntax
BEGIN
{sql_statement | statement_ block}
END

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Identify how to display the required messages (Contd.)
Result:
The messages can be displayed using the PRINT and
IF…ELSE statements in a batch

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Draft the batch on paper
Result:
The batch statements are shown below.
DECLARE @iTest int
SELECT @iTest = siTestScore FROM
InternalCandidate
WHERE cEmployeeCode = '000008'
IF @iTest 80
PRINT 'Rejected - Not called for interview'
ELSE
BEGIN
PRINT 'Called for interview'
PRINT 'your test score ='
PRINT @iTest
END
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Execute the batch
Action:
In the Query Analyzer window, type the statement given
below.
DECLARE @iTest int
SELECT @iTest = siTestScore
FROM InternalCandidate
IF @iTest 80
PRINT 'Rejected - Not called for
interview'

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Execute the batch (Contd.)
ELSE
BEGIN
PRINT 'Called for interview'
PRINT 'your test score ='
PRINT @iTest
END
Press F5 to execute the batch

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Verify the batch
Action:
Verify your answer by executing the following query:
SELECT siTestScore
FROM InternalCandidate

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More Constructs
The CASE Statement
In situations where several conditions need to be
evaluated, SQL Server provides a programming construct
called the CASE statement
Syntax
CASE
WHEN boolean_expression THEN expression
[[WHEN boolean_expression THEN
expression] [...]]
[ELSE expression]
END
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More Constructs (Contd.)
The WHILE Statement
You can use the WHILE construct in a batch, a stored
procedure, a trigger, or a cursor to allow a set of T-SQL
statements to execute repeatedly as long as the given
condition holds true
Syntax
WHILE boolean_expression
[BREAK]
[CONTINUE]
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More Constructs (Contd.)
The BREAK and CONTINUE Statements
You can use the BREAK and CONTINUE statements to
control the execution of the statements inside a WHILE
loop
The BREAK statement causes an exit from the WHILE
loop
The CONTINUE statement causes the WHILE loop to
restart, skipping any statements after CONTINUE inside
the loop

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Summary
In this lesson, you learned that:
A view is a virtual table, which consists of a subset of columns
from one or more tables
A view derives its data from one or more tables known as base
or underlying tables
Views serve as security mechanisms, thereby protecting data
in the base tables
A view can restrict access to data in specific columns, specific
rows, specific rows and columns, rows fetched by using joins,
statistical summary of data in a given table, subsets of another
view or a subset of views and tables
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Summary (Contd.)
A view can be created with the CREATE VIEW statement
SQL Server allows data to be modified only in one of the
underlying tables when using views, even if the view is derived
from multiple underlying tables
A view can be modified with the ALTER VIEW statement
A view can be dropped with the DROP VIEW statement
A view can be renamed with the sp_rename stored procedure
A batch is a set of SQL statements submitted together to the
server for execution
You can use a variable to store a temporary value
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Summary (Contd.)
You can use the PRINT statement to display a user-defined
message or the content of a variable on the screen
You can use the comment entries in batches to write a
description of the code
You can use the IF…ELSE statement for conditional execution
of SQL statements
The CASE statement evaluates a list of conditions and returns
one of the various possible results
You can use the WHILE statement in a batch to allow a set of
T-SQL statements to execute repeatedly as long as the given
condition holds true
©NIIT


Summary (Contd.)
The BREAK statement causes an exit from the WHILE loop
The CONTINUE statement causes the WHILE loop to restart,
skipping any statements after CONTINUE inside the loop

©NIIT

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