08 CSharp Lesson Transcript

7/28/2019 08 CSharp Lesson Transcript

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Lesson:08

Obtaining Data from a SQL 2005 Express Edition Database

In this video we will briefly talk about databases, specifically how to work with SQL2005

Express Edition databases. But before we run, we need to walk. So we will start off by

talking about databases: what they are, why you use them, and how they are structured. And

then we will demonstrate how to create and use the SQL2005 Express Edition database from

within Visual C sharp, and finally I will demonstrate how to modify data that is stored in a

SQLdatabase. So lets start small. What is a database? Well simply put, it is a structured

repository for data. You save information in a database you, read the information from the

database, you update the information, and sometimes you need to delete the information. The

information is organized so it can be retrieved easily, can be sorted, can be grouped, can be

related to other data, and thereby can be used to analyze information in a countless number of

ways.

So lets say you have a business and you want to keep track of your customers. You could

store customer names in simple text files using notepad. But the problem is that after a while,

there are so many names that it becomes unmanageable, and you have to scroll through this

long file to find the name of the customer that you need to follow up with. So you decide to

store the names of the customers in an Excel spreadsheet instead, which works for a while,

but what happens when you want to view all the purchases in the month of April for your top

ten customers? Well I suppose that it is possible in Excel, but it is not as easy as using a

Relational Database Management System or RDBMS like SQLServer. And this is just the tip

of the iceberg in terms of benefits in using the real database over a text file or an Excel

spreadsheet. It is probably the most easy way to understand it though. Now up to now,

SQLwas considered a high-end database server used in large companies to enable the

management and the retrieval of relational database data. In SQL2005 Express Edition,

however, you can harness the power in the most simple applications that you can dream up.

[Start: 00:00:00 & End: 00:02:05]

Now, were using the term RDBMS or Relational Database Management System. This is

actually a philosophy or an approach to designing a database that is analogous in some ways

to writing object-oriented code, although it is very different, different techniques, different

goal, etc. But in Relational Database theory, you organize your data into table that are related

with other tables and so on. So you might dedicate a table for customer names, and another


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table for order information. Now, you could just create one table that contains both customer

and order information. But then you run the possibility of having redundant information

when you have a customer that orders twice. And then there is also the issue of data integrity.

What if the customer called himself Bob on the first order and Robert on the second

order? Or a better example might be if the customer moved. It would be difficult to

determine that both orders were, in fact, from the same customer. So it makes sense to

manage this information in separate tables. Now, there are really a lot of rules that were

created back in the 1970s and the 1980s by the creator of Relational Database theory, and

those rules are called normalization. And were not going to take the time to go over the

rules, but be aware that Ive really just skimmed over this idea, and you can find out a lot

more on your own. In most cases, you can normalize the database with just a little common

sense. Once you see it done a few times, it is going to make a lot more sense to you. You

will pretty much have the idea on it.

So lets dig deeper into database objects. First of all, please take the time to read the

document that I have supplied that accompanies these videos, because it is going to have

some additional information that will supplement what I say here.

So were going to start with the concept of a table. And a table is the foundational database

object. A table consists of columns and rows, or rather records.

[Start: 00:02:05 & End: 00:04:01]

A single column in a single row is often referred to as a field of data. The columns define the

type of data that will be stored in the table, and the rows or records are the actual data. So we

might have a simple customer table with the following columns: first name, last name,

address, state, ZIP, credit limit, customer since, and so on. We have probably left out a

number of fields that should belong in there as well. But, I think you get the idea. In order to

maintain data integrity, we need to define more information about each column, such as the

type of data that is going to be stored in that column, and in some cases, like for example,

string data, were going to have to define the maximum number of characters in the string.

Well also need to define if a particular record can be saved, if it contains fields of

information with null data.


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easily managed. It reduced redundant data by splitting up duplicate data into its own tables,

and it helps to maintain the integrity of the data among other things.

So lets now transfer this to databases into creating SQL2005 database. Then were going to

add objects like tables and fields and relations to the database, and then finally, we will add

some data to it.

So I have taken the liberty of creating a new project called lesson 08, and I just want you to

know that there are actually several different ways that you can go about creating a new

SQLExpress 2005 database. But Im going to use a more project-base approach for this

example.

[Start: 00:09:55 & End: 00:12:04]

So with my project open, Im going to right-click on my project, and select add new item.

And from the install template section, Im going to select a SQLdatabase. And then Im

going to change the name of the database to lesson08.mdf, and select add. Now by default,

it is going pop open this data source configuration wizard. Lets not worry about this for right

now. Im just going to select the cancel button, and then Im going to double-click this file

within the solution explorer so that I can open up the database explorer with my database

already loaded in. Now you can see here that there are some files underneath the lesson

08.mbf file that is loaded under the data connections node. What we want to concentrate on

are tables, and by default, there are going to be no tables in the database. But what I want to

do is right-click and select add new table. Lets reposition a things here so we can see the

main area a little better. Now we have a designer surface where we can create a new table,

and were going to be forward looking, and create two tables that will be eventually used

within our RSS reader application. We will create them again in the future, but just so we can

have something to talk about, were going to create a folder table, and then were going to

create a channel table. Lets start with the folder table. So Im going to put my cursor in this

little box next to column name, and Im going to create a folder ID, which Im going to use as

my primary key for this table. For the data type, Im going to put my mouse cursor in the data

type column, and then Im going to use the little combo box, and find the integer data type.

[Start: 00:12:04 & End: 00:14:14]


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And then Im going to deselect allow nulls. I do not want this field to allow any nulls.

Now if you remember from discussion a few moments ago, whenever you are creating

primary key, were going to set a special property of this column called the identity property,

which will automatically number each row of data or each record of data that is added to this

table. So to turn on that automatic numbering, what were going to need to do is scroll down

in this column properties tab, and find the identity specification. And Im just going to

double-click it. I need to open this up, right. It is the identity, were going to turn this to

yes. Now there are some other things, identity increment and identity seed. Do not worry

about those. Just leave them at their defaults for right now. And then,I want you to select in

the next row where were defining columns, and were going to create a second column called

folder name, and this time you can see that it defaults to nchar[10]. What we want to do is

place textual information, and allow up to 50 characters, and allow it to be nullable. So were

going to select this nvarchart[50]. Were going to turn off the null, allow null for right now.

And that is about all we need to do with one exception. Right now, even though we have

defined our primary key, we have not told the database that we intend for this column to be

used for that purpose. So what we will do is select this little button on our toolbar to set the

primary key.

[Start: 00:14:14 & End: 00:16:00]

And when I do, notice that there is a little key that is added right next to the folder ID column.

Im going to select the save button on my toolbar, and it asked me to choose a name for my

table. I do not want table 1 to be the name of this table. I want something a little more

descriptive. Im going to call this table folder. Select the OK button, and now as you can

see in the database explorer on the left-hand side, a new table has been created called

folder, and I can even drill down to see all the columns that are related to this folder, folder

ID and folder name. When I select either of these columns, notice over on the right-hand side

in the property window, we can view properties about that column. Now, we cannot change it

here. It is all grayed out. But we can still see some information about, for example, the folder

ID, whether it is an identity or not, the length and so on. So we have created our first table.

Lets now close this designer, and we will just close everything. We will go back to tables,

and were going to create a second table. Add new table, and Im going to do this a little bit

quicker this time since I walked you through it slowly last time. And this is going to be a

table that will hold the channels. We will talk about this when we get to the RSS reader

application. We want to make this an integer, and turn off nulls. And I also want to set it as


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my primary key. Our channel will need a title. So Im going to go to nvarchar[50], and I

want to change it from a length of 50, by default, to a length of lets say, 250. So that will

allow me to put up to 250 characters of data, of string data in this column. Now, I also want

to not allow it to accept any rows. I think I may have made a mistake in my channel. As I

remember, I did not turn on the identity column. So Im going to go back, go to my is

identity property, and select yes. Now, we will continue on. Channel will need a URL, and

once again, Im going to use the nvarchar, but Im going to change it from 50 to a length of

250, and Im not going to allow it to be null. Or actually, in this case, I will go ahead and

allow it to be null, and finally, Im going to need to create foreign key back to the folder table,

because we want there to be a relationship between the folder table and our new channel table

that were creating. Folder ID, in this case, we want an integer and were not going to allow it

to accept nulls. I think I got it right. So when I select save, it is going to ask me for a

name, and we will call this channel, and select OK.

[Start: 00:16:00 & End: 00:19:04]

So as you can see, I now have a second table here with four columns defined. And we can

move on to the next bit of business, which is to create a relationship between these two tables.

Now, there are actually several different ways that we can go by creating these relationships.

There is a straightforward way and then there is a more visual way that we can do it. And Im

going to take the more fun, visual approach for this first time. And to do that, Im going to

create a database diagram. So over here in my database explorer, Im going to select

database diagram. So Im going to right-click and select add new diagram. It is going to

say that it does not have one or more of the database objects required to use database diagram.

You should create them, select yes, and give it a moment or two. And then it is going to

pop up and ask for the tables that you want to add to this diagram. We want both of these

added. So Im going to select the add button once, and select it a second time, and then

click the close button, and now what you can see is kind of a visual view of the table that I

have selected, the two tables that are in my database. Now the way that you create a

relationship between these two tables is really simple. All you have have to do is put your

mouse cursor over the first one, kind of in this gray area, and hold down and drop it in its

corresponding primary key in the other table. And when you do, it pops open some dialogue

boxes. We could have used this dialogue-based approach to create it in the first place, but I

thought it will be fun to create a database diagram, but either way, we have to go through the

same steps at this point. So it is just that these are filled in automatically for us. The primary


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key table on the left-hand side is folder, and the primary key itself is the folder ID, and then

you can see over in the foreign key tables, the channel table and the foreign key column itself

is the folder ID. That looks correct.

[Start: 00:19:04 & End: 00:21:10]

Notice that it gave it a default name of fk_channel_folder. That looks good so I wont change

that, and select the OK button, and Im going to select OK a second time, and Im going

to save this whole project and everything including the tables. And I need to give it a diagram

name, diagram 0 is just fine. And after it asks us all these questions, we should be in good

shape now. I have expanded the data connections one more time to get back. You can see I

have now my diagram. I have my tables. And I know that I have a relationship between

those two tables.

So the next order of business is to start adding data to our table. Lets do this: Lets first of all

start with our folder, and were going to right-click it. And were going to select show table

data. And in the main area it will what looks like a grid. Notice at the very top we have

columns, and what were going to do start typing in data for the rows. So folder name, were

going to call this first folder, and then Im going to use my tab key on my keyboard, and

notice that it automatically put 1 in the folder ID for my first record of my first row of data,

and then use the tab key again because I do not want to mess with the folder ID. It is going

to automatically number itself. So here I will put second folder, and notice as Im making a

modification to a given record or a given row, that on the left-hand side I get this little pencil

that looks like it is editing, and that is what we were doing. Were editing or making a

modification to the row. And once again, here were going third folder, and so on.

[Start: 00:21:10 & End: 00:23:16]

So we have added three rows of data to our database. Now we can use these little navigation

buttons here at the bottom. We can move to the first row, and notice the little arrow cursor

goes to the first row of data. Notice that I can go to use these next buttons, and the

next/previous buttons will let me go one at a time, or I can use this move to the last row of

data, and I can also select to move to a new row. So it automatically places me at the

position or I can add yet a fourth folder and so on. I can also just type in a number and hit the

enter key on my keyboard, and it puts me to that row of data in my database. So I have

made modifications to my data. If I want to change something, and just for example make a


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changes. So right now, it looks like it is going to let us, and then we get an error message

that says, delete statement conflicted with the reference constraint, FK channel folder.

[Start: 00:25:58 & End: 00:27:50]

So you can see that in order to maintain data integrity, the database is not going to allow us to

delete a row from the folder that would, in essence, create orphan tables, or orphan rows

rather, in my channel table.

At this point you might get tired hearing what Im about to say, but we have really just

scratched the surface of working with tables, and columns, and records, and constraints with

the SQL2005 Express Edition database. And you might be wondering, what are we going to

do with this data? How does it really benefit us to put all this data in the database? In the

next couple of videos, were going to look at how to enter and retrieve the data from and to

the database using a Windows application. So were going to be able to represent the data in

a grid or in textboxes, make changes, and save them back to the database. This is when it

actually all starts coming together, and starts becoming a lot of fun. So just hang in there.

Were almost to some things that will really allow you to create powerful applications.

Were going to stop here for right now. If you enjoyed watching this video, please visit

www.learnvisualstudio.net to download and watch over 500 videos just like this one aimed at

all skill levels on many different topics related to C#, Visual Basic.NET, ASP.NET and more.

Thank you.

[Start: 00:27:50 & End: 00:02:05]
http://www.learnvisualstudio.net/http://www.learnvisualstudio.net/

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