SQL: Views and Advanced Stored Prcedures

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National University of Computer and Emerging Sciences

Lab Manual 8Views and Stored Procedures(Advanced Concepts)

Database Systems

Lab Instructor(s) Anam MansoorSemester Spring 2014

Department of Computer Science

FAST-NU, Lahore, Pakistan


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Table of Contents

1. Task Distribution ........................................................................................................................................... 3

2. Objective ....................................................................................................................................................... 4

3. Views ............................................................................................................................................................. 5

Use of a View .................................................................................................................................................... 6

General syntax for Views .................................................................................................................................. 6

Creating a View ............................................................................................................................................. 7

Get result from a View .................................................................................................................................. 7

Drop a View ................................................................................................................................................... 7

4. Advanced Stored Procedures ...................................................................................................................... 12

Modifying an Existing Stored Procedure ........................................................................................................ 12

Using try catch in SQL Server stored procedures ........................................................................................... 13Reducing amount of network data for SQL Server stored procedures .......................................................... 13

Deleting a SQL Server stored procedure......................................................................................................... 15

5. Exercise ........................................................................................................................................................... 16

6. References ...................................................................................................................................................... 17


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FAST NU Lahore Database Systems CS 204

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1. Task DistributionTotal (170 minutes)

o Views (35 minutes)o Stored Procedures (Advanced Concepts) (35 minutes)o In lab Exercise (60 minutes)o Phase 2 Evaluations (30 minutes)


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2. ObjectiveIn this lab, the concept of views will be discussed along with its implementation and types. We will also go

through introduce some advance usage of stored procedures. At the end of this lab, you will have knowledge

of the following.

o Views.o Advanced Concepts of stored procedures.


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3. ViewsA database viewdisplays one or more database records on the same page. A view can display

some or all of the database fields. Views havefiltersto determine which records they show.

Views can be sortedto control the record order and groupedto display records in related sets.

Views have other options such as totals and subtotals.

Most users interact with the database using the database views. A key to creating a useful

database is a well-chosen set of views. Luckily, while views are powerful, they are also easy to

create.

A View is a "Virtual Table". It is not like a simple table, but is a virtual table which contains columns and data

from different tables (may be one or more tables). A View does not contain any data, it is a set of queries

that are applied to one or more tables that is stored within the database as an object. After creating a view

from some table(s), it used as a reference of those tables and when executed, it shows only those data whichare already mentioned in the query during the creation of the View.


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In the above diagram, we have created a View (View_Table1_Table2) from Table1 and Table2. So the

View_Table1_Table2 will only show the information from those columns. Let's checkout the basic syntax for

creating a View:

CREATE VIEW [View Name]

AS

[SELECT Statement]

Use of a View

Views are used as security mechanisms in databases. Because it restricts the user from viewing certain

column and rows. Views display only those data which are mentioned in the query, so it shows only data

which is returned by the query that is defined at the time of creation of the View. The rest of the data is

totally abstract from the end user.

Along with security, another advantage of Views is data abstraction because the end user is not aware of all

the data in a table.

General syntax for Views

In this section, I will describe how to create Views, select data from Views, and deleting Views. I have created

a database named ViewDemo. It has a table called EmpInfoas shown below:

which contains the following data:

All the examples I have described are from this database.


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Creating a View

Below is the general syntax for creating a View:

CREATE VIEW [View_Name]AS[SELECT Statement]

For example:

CREATEVIEWSampleViewAsSELECTEmpID,EmpName FROMEmpInfo

which will create a View with the name SampleView that will only contain EmpID, EMPName.

Get result from a View

This is similar to a Select statement:

select*fromSampleView

Now have a look at the output of SampleView:

Drop a View

DROPVIEWSampleView

Now if we want to select data from SampleView, we will get the following error:


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We begin with creating 3 tables PRODUCTS, Customer & BOOKING. These are fictitious tables for our demo.

The PRODUCTS stores data for a retail shop with a flag column IsSalable based on whose value we treat the

products as Salable.

CREATETABLEPRODUCTS(ProductID INTPRIMARYKEYCLUSTERED,ProductDesc VARCHAR(50)NOTNULL,

ManufacturingDate DATETIME,ExpiryDate DATETIME,IsSalable BIT,--1 Salable/Active FOR 0 For NonSalable/Passive ProductPrice MONEYNOTNULL)

Next, we have a Customer table which stores UserID and Password details for customers.

CREATETABLECustomer(CustID INTIDENTITY(1002,2)PRIMARYKEYCLUSTERED,FName VARCHAR(50)NOTNULL,LNme VARCHAR(50)NOTNULL,

UserID VARCHAR(100)NOTNULL,Pswd NVARCHAR(100)NOTNULLDEFAULT'password123')

Lastly, I have created a BOOKING table which houses all the bookings from different customers.

CREATETABLEBOOKING(BookingID INTIDENTITY(10,2)PRIMARYKEYCLUSTERED,ProductID INTREFERENCESdbo.Products(ProductID),CustID INTREFERENCESdbo.Customer(CustID),DateOfBooking DATETIMENOTNULL,QTY INT

)

Next, insert a few records into these tables:

INSERTINTOPRODUCTS VALUES(1,'Biscuits','2011-09-01 00:00:00.000','2012-09-01 00:00:00.000',1,20)INSERTINTOPRODUCTS VALUES(2,'Butter','2010-09-01 00:00:00.000','2011-09-01 00:00:00.000',1,30)


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INSERTINTOPRODUCTS VALUES(3,'Milk','2011-10-01 00:00:00.000','2011-11-01 00:00:00.000',1,46)

INSERTINTOCustomer(FName,LNme,UserID,Pswd)

VALUES('Sara','Verma','[email protected]','S123')INSERTINTOCustomer(FName,LNme,UserID,Pswd)VALUES('Rick','Singh','[email protected]','G311')INSERTINTOCustomer(FName,LNme,UserID,Pswd)VALUES('Micky','Khera','[email protected]','M222')

INSERTINTOBOOKING(ProductID,CustID,DateOfBooking,QTY)VALUES(1,1002,'2011-11-01 00:00:00.000',3)INSERTINTOBOOKING(ProductID,CustID,DateOfBooking,QTY)

VALUES(2,1004,GETDATE(),4)INSERTINTOBOOKING(ProductID,CustID,DateOfBooking,QTY)VALUES(3,1006,'2011-10-01 00:00:00.000',2)

Our table contents look like this. I know the tables are not completely normalized, for now please ignore

them, these are simple demo tables.

SELECT*FROMCustomer

Select*fromPRODUCTS

Select*fromBOOKING

A customer purchases/books a product and the same gets recorded into the BOOKING table now to generate

the bill on his name we can uses a VIEW which would help us do away with a physical table. Instead it would

enable us to generate the bill based on the information from these 3 tables itself. Lets see how its possible.

CREATEVIEWBill_VASSELECTC.FName

,C.LNme,P.ProductDesc,B.DateOfBooking,P.Price,B.QTY,(B.QTY*P.Price)ASTotalAmountPayable

FROMBOOKING BINNERJOINPRODUCTS PONB.ProductID=P.ProductIDINNERJOINCustomer CONB.CustID=C.CustID;


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Next if,

Select*fromBill_V

Now we will create another view

CREATE VIEWv_EmployeeDetailAS

SELECT E.EmployeeID,E.Name,EA.AddressLine1,EA.CityFROM Employee E

INNERJOINEmployeeAddress EAONEA.EmployeeID =E.EmployeeID

SELECT *FROMv_EmployeeDetail

Views WITH CHECK OptionTo restrict the changes that users can make, you use the CREATE VIEW commands WITH CHECK OPTION

clause when defining the view

CREATE VIEWv_EmployeeDetailWithCheckOptionASSELECTE.*

FROMEmployee EWHEREE.EmployeeID


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-- inserting into viewwould add automatically to the table--

INSERTINTOv_EmployeeDetailWithCheckOption(EmployeeID,NAME)

VALUES(12,'Added with View')

SELECT*FROMEmployeeSELECT*FROMv_EmployeeDetailWithCheckOption

---- Out OF Range

--inserting into tablewould be allowed but would not reflect into view as its against the view check--

INSERTINTOEmployee(EmployeeID,NAME)VALUES(16,'Added with Table')


-- inserting into viewwould not be allowed--

INSERTINTOv_EmployeeDetailWithCheckOption(EmployeeID,NAME)VALUES(17,'Added with View')


-- DELETE Employee WHERE employeeid= 16


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4. Advanced Stored ProceduresModifying an Existing Stored Procedure

Overview

when you first create your stored procedures it may work as planned, but how to do you modify an existing

stored procedure. In this topic we look at the ALTER PROCEDURE command and it is used.

Explanation

Modifying or Altering a stored procedure is pretty simple. Once a stored procedure has been created it is

stored within one of the system tables in the database that is was created in. When you modify a stored

procedure the entry that was originally made in the system table is replaced by this new code. Also, SQL

Server will recompile the stored procedure the next time it is run, so your users are using the new logic. Thecommand to modify an existing stored procedure is ALTER PROCEDURE or ALTER PROC.

Let's say we have the following existing stored procedure: This allows us to do an exact match on the City.

Let's say we want to change this to do a LIKE instead of an equals.

To change the stored procedure and save the updated code you would use the ALTER PROCEDURE command

as follows.


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Now the next time that the stored procedure is called by an end user it will use this new logic.

Using try catch in SQL Server stored procedures

Overview

A great new option that was added in SQL Server 2005 was the ability to use the Try..Catch paradigm that

exists in other development languages. Doing error handling in SQL Server has not always been the easiest

thing, so this option definitely makes it much easier to code for and handle errors.

Explanation

If you are not familiar with the Try...Catch paradigm it is basically two blocks of code with your stored

procedures that lets you execute some code, this is the Try section and if there are errors they are handled in

the Catch section.

Let's take a look at an example of how this can be done. As you can see we are using a basic SELECTstatement that is contained within the TRY section, but for some reason if this fails it will run the code in the

CATCH section and return the error information.

Reducing amount of network data for SQL Server stored procedures


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Overview

Their are many tricks that can be used when you write T-SQL code. One of these is to reduce the amount of

network data for each statement that occurs within your stored procedures. Every time a SQL statement is

executed it returns the number of rows that were affected. By using "SET NOCOUNT ON" within your stored

procedure you can shut off these messages and reduce some of the traffic.

Explanation

As mentioned above there is not really any reason to return messages about what is occurring within SQL

Server when you run a stored procedure. If you are running things from a query window, this may be useful,

but most end users that run stored procedures through an application would never see these messages.

You can still use @@ROWCOUNT to get the number of rows impacted by a SQL statement, so turning SET

NOCOUNT ON will not change that behavior.

Not using SET NOCOUNT ON

Here is an example without using SET NOCOUNT ON

The messages that are returned would be similar to this:

This example uses the SET NOCOUNT ON as shown below. It is a good practice to put this at the beginning of

the stored procedure.

Using SET NOCOUNT ON

This example uses the SET NOCOUNT ON as shown below. It is a good practice to put this at the beginning of

the stored procedure.


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Using SET NOCOUNT ON and @@ROWCOUNT

This example uses SET NOCOUNT ON, but will still return the number of rows impacted by the previous

statement. This just shows that this still works.


Deleting a SQL Server stored procedure

Overview

In addition to creating stored procedures there is also the need to delete stored procedures. This topic

shows you how you can delete stored procedures that are no longer needed.

Explanation

The syntax is very straightforward to drop a stored procedure, here are some examples.

Dropping Single Stored Procedure

To drop a single stored procedure you use the DROP PROCEDURE or DROP PROC.


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Dropping Multiple Stored Procedures

To drop multiple stored procedures with one command you specify each procedure separated by a comma as

shown below.

5. ExerciseLoad the employee management schema (TableScripts.sql) before attempting this exercise.

1. Create a view of all employees against their RateChangeDate field in EmployeePayHistory.2. Create a view that displays all employeeDetails from Employee table against their respective

Maximum ratechangeDate in EmployeePayHistory table.

e-g

EmployeeID RateChangeDate

4 1998-01-05 00:00:00.000

4 2000-07-01 00:00:00.000

4 2002-01-15 00:00:00.000

So from this record set Employeeid would qualify for third row where RateChangeDate = 2002-01-15

00:00:00.000.

Accordingly you should select maximum ratechangeDate of any employee with >1 rateChangeDate.

Rest of the single row employee would be taken as it is.

Output should be All employee details from Employee and Maximum RateChageDate as

LatestRateChangeDate from EmployeePayHistory.

3. Create a view that displays total number of employees who have been associated with thedepartment (END Date not null) .You have to display departmentid and count of employee with an


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additional filter of Employee Count >1. There are 2 filters that need to be adjusted so make sure you

adjust them properly i-e EndDate, Count check

4. Create a view having all the details of an employee and his average salary of year 20085. Create a view that should restrict the data domain in the table VIEW_EmployeePayHistory with

EmployeeID >20 and DaysPerWeek < 7

You have to show the result before the insertion of any record and then the table and view state

after the insertion of valid record (within the domain check) and also out of range data.

6. Create a stored procedure that tries to delete product with any id from the products table. If a foreignkey constraint fails then this store procedure should print an error message( This will be checked for

both the cases i) When the product can be deleted ii) When the foreign key constraint fails )

6. References

1. http://www.mssqltips.com/sqlservertutorial/160/sql-server-stored-procedure/
http://www.mssqltips.com/sqlservertutorial/160/sql-server-stored-procedure/http://www.mssqltips.com/sqlservertutorial/160/sql-server-stored-procedure/http://www.mssqltips.com/sqlservertutorial/160/sql-server-stored-procedure/

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