sql xp 08

©NIITSQL/Lesson 8/Slide 1 of 50

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



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



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



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.cPositionCode



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'



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.



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



Identify how to simplify queries Result:

Simplification of the query can be done using views



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



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]



Create the view (Contd.)

Action:

In the Query Analyzer window, type:CREATE VIEW vwEmpSkillASSELECT vFirstName, vLastName, vQualification, vSkill

FROM Employee JOIN PositionSkillON Employee.cCurrentPosition = PositionSkill.cPositionCode

JOIN SkillON PositionSkill.cSkillCode = Skill.cSkillCode

Press F5 to execute the command



Verify that the queries have been simplified by executing the required queries on the view

Action:

In the Query Analyzer window, type:

SELECT vFirstName, vSkill FROM vwEmpSkill

Press F5 to execute the query


SELECT vFirstName, vLastName, vSkill

FROM vwEmpSkill




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




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





Just a Minute (Contd.)

SELECT vFirstName, vAddress, cCity, cZip, cDesignation, vDepartmentName, vDepartmentHead



WHERE cCity = 'Columbus'

Simplify the task of executing these queries.



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]



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



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



8.D.2 Modifying Data Using Views

A view is defined as follows:CREATE VIEW vwEmployeeCandidateASSELECT Employee.cCandidateCode, vFirstName, vLastName, cPhone, siTestScoreFROM Employee JOIN InternalCandidateON Employee.cCandidateCode=InternalCandidate. cCandidateCode



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=75WHERE cCandidateCode=‘000018’

Identify the error and correct it so that data in the tables is modified.



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



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



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



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:UPDATE vwEmployeeCandidate

SET siTestScore=75 WHERE cCandidateCode='000018'



Update tables

Action:


UPDATE vwEmployeeCandidate SET cPhone = '(614)324-5634' WHERE cCandidateCode = '000018'

UPDATE vwEmployeeCandidate

SET siTestScore = 75 WHERE cCandidateCode = '000018'

Press F5 to execute the statement



Verify that the tables have been updated

Action:

In the Query Analyzer window, type:SELECT * FROM Employee WHERE cCandidateCode = '000018'

SELECT * FROM InternalCandidateWHERE cCandidateCode = '000018'

Press F5 key to execute the queries



8.P.1 Modifying Data Using Views

A view was defined as follows:CREATE VIEW vwNewspaperNewsadASSELECT cNewspaperName,vCity,cZip,dAdStartDateFROM Newspaper JOIN NewsAdON Newspaper.cNewspaperCode =NewsAd.cNewspaperCode

The following statement, when given to update the table, did not update the table:UPDATE cNewspaperNewsAdSET cZip='88993-4532',dAdStartDate='01/09/99'WHERE cNewspaperName='Daily News'

Modify data in the base tables.



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



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




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




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



Programming for SQL Server (Contd.) 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)




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



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.



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.



Task List

Identify how to display the required messages

Draft the batch on paper

Execute the batch

Verify the batch



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}]



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

SyntaxBEGIN

{sql_statement | statement_ block}END



Identify how to display the required messages (Contd.)

Result:

The messages can be displayed using the PRINT and IF…ELSE statements in a batch



Draft the batch on paper

Result:

The batch statements are shown below.DECLARE @iTest intSELECT @iTest = siTestScore FROM InternalCandidateWHERE cEmployeeCode = '000008'IF @iTest < 80PRINT 'Rejected - Not called for interview'ELSEBEGIN PRINT 'Called for interview' PRINT 'your test score =' PRINT @iTestEND



Execute the batch

Action:

In the Query Analyzer window, type the statement given below.DECLARE @iTest intSELECT @iTest = siTestScore FROM InternalCandidateWHERE cEmployeeCode = '000008'IF @iTest < 80 PRINT 'Rejected - Not called for interview'



Execute the batch (Contd.)

ELSEBEGIN PRINT 'Called for interview' PRINT 'your test score =' PRINT @iTestEND

Press F5 to execute the batch



Verify the batch

Action: Verify your answer by executing the following query:

SELECT siTestScoreFROM InternalCandidate WHERE cEmployeeCode = '000008'



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



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 {sql_statement | statement_block}[BREAK]{sql_statement | statement_block}[CONTINUE]



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



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



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



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



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

sql xp 08

Technology

views sqllesson

views contd

tables views

view sqllesson

subset of views

renaming views

view action

views update data