SQL Server 2008 Essential Training
Illustration by Mark Todd

Defining keys


SQL Server 2008 Essential Training

with Simon Allardice

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Video: Defining keys

One thing you should do on all of your tables, at least as a general rule, is defined what's called a primary key. This is a way that's going to identify how do we get to an individual role. One value that would always take us to just one row in that table. And your primary key can be any of the columns that you actually have defined if that makes sense. Sometimes it does, sometimes it doesn't. If I look at my Product Table, for example I have ProductID, ProductName, UnitPrice and UnitsInStock, and let's say that my business process was such that ProductIDs were decided around a conference table and manually entered into the database.
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  1. 2m 21s
    1. Welcome
      1m 19s
    2. Using the exercise files
      1m 2s
  2. 17m 58s
    1. SQL Server core concepts
      9m 4s
    2. SQL Server editions
      3m 8s
    3. Applications included with SQL Server
      5m 46s
  3. 26m 1s
    1. Preparing for installation
      3m 44s
    2. Creating service accounts
      2m 33s
    3. Installing SQL Server
      11m 42s
    4. Post-installation checks
      3m 9s
    5. Installing sample databases
      4m 53s
  4. 13m 35s
    1. Introduction to SQL Server Management Studio
      8m 7s
    2. Introduction to SQL Server Books Online
      3m 6s
    3. SQL Server system databases
      2m 22s
  5. 1h 26m
    1. Planning your database
      9m 39s
    2. Creating a SQL Server database
      4m 7s
    3. Creating tables
      7m 51s
    4. Data types in SQL Server
      12m 25s
    5. Defining keys
      8m 9s
    6. Creating default values
      4m 39s
    7. Creating check constraints
      2m 25s
    8. Creating unique constraints
      4m 34s
    9. Introduction to relationships and foreign keys
      9m 51s
    10. Creating relationships in SQL Server Management Studio
      8m 14s
    11. Database normalization
      11m 47s
    12. Creating computed columns
      3m 10s
  6. 23m 11s
    1. Using the SQL Server Import and Export Wizard
      3m 58s
    2. Importing Excel files into SQL Server
      6m 11s
    3. Importing CSV files into SQL Server
      5m 27s
    4. Importing Access databases into SQL Server
      7m 35s
  7. 55m 29s
    1. Introduction to Transact-SQL
      3m 43s
    2. Using SELECT statements
      7m 16s
    3. Changing the default database
      2m 21s
    4. Creating conditions in SQL
      8m 10s
    5. Sorting your output
      3m 23s
    6. Using aggregate functions
      7m 12s
    7. Finding unique values
      2m 14s
    8. Using subqueries
      9m 33s
    9. Joining multiple tables together
      8m 0s
    10. Viewing execution plans
      3m 37s
  8. 19m 36s
    1. Writing INSERT statements
      5m 47s
    2. Writing UPDATE statements
      4m 38s
    3. Writing DELETE statements
      2m 54s
    4. Using the OUTPUT clause to return inserted keys and GUIDs
      6m 17s
  9. 32m 52s
    1. Introduction to SQL functions
      6m 26s
    2. Using SQL configuration functions
      2m 14s
    3. Using string functions
      7m 26s
    4. Using date functions
      6m 27s
    5. Creating user-defined functions
      10m 19s
  10. 28m 46s
    1. Introduction to stored procedures
      4m 23s
    2. Creating stored procedures
      11m 23s
    3. Introducing transactions
      4m 23s
    4. Creating transactions
      8m 37s
  11. 16m 39s
    1. Understanding and creating indexes
      6m 32s
    2. Monitoring and rebuilding indexes
      6m 0s
    3. Monitoring database size and integrity
      4m 7s
  12. 11m 41s
    1. Creating backups
      4m 21s
    2. Creating differential backups and using backup compression
      3m 40s
    3. Restoring databases
      3m 40s
  13. 17m 40s
    1. Introduction to SQL Server security and permissions
      5m 54s
    2. Adding a Windows user to the database
      5m 7s
    3. Creating SQL Server logins and switching authentication modes
      6m 39s
  14. 36m 41s
    1. Introduction to SQL Server Reporting Services
      2m 52s
    2. Connecting to the Report Manager
      4m 29s
    3. Using Report Builder
      12m 4s
    4. Formatting values in reports
      4m 17s
    5. Adding indicators to reports
      5m 11s
    6. Adding charts to reports
      3m 54s
    7. Working with report security
      3m 54s
  15. 24m 41s
    1. Introduction to SQL Server Integration Services (SSIS)
      1m 57s
    2. Using Business Intelligence Development Studio (BIDS)
      6m 59s
    3. Creating and executing a simple SSIS package
      7m 35s
    4. Importing packages into SQL Server Management Studio
      3m 21s
    5. Scheduling jobs with SQL Server Agent
      4m 49s
  16. 31s
    1. Goodbye

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Watch the Online Video Course SQL Server 2008 Essential Training
6h 54m Beginner Dec 15, 2010

Viewers: in countries Watching now:

In SQL Server 2008 Essential Training, Simon Allardice explores all the major features of SQL Server 2008 R2, beginning with core concepts: installing, planning, and building a first database. Explore how Transact-SQL is used to retrieve, update, and insert information, and gain insight into how to effectively administer databases. The course also covers features outside SQL Server's database engine, including technologies that have grown up around it: SQL Server Reporting Services and Integration Services. Exercise files are included with the course.

Topics include:
  • Using T-SQL (Transact-SQL)
  • Managing databases with SQL Server Management Studio
  • Understanding database normalization
  • Using SELECT statements
  • Building indexes
  • Monitoring database size and integrity
  • Backing up and restoring databases
  • Creating functions and stored procedures
  • Managing database permissions
  • Creating and formatting reports
  • Adding charts to reports
  • Creating and executing a simple SSIS package
Business Developer IT
SQL Server
Simon Allardice

Defining keys

One thing you should do on all of your tables, at least as a general rule, is defined what's called a primary key. This is a way that's going to identify how do we get to an individual role. One value that would always take us to just one row in that table. And your primary key can be any of the columns that you actually have defined if that makes sense. Sometimes it does, sometimes it doesn't. If I look at my Product Table, for example I have ProductID, ProductName, UnitPrice and UnitsInStock, and let's say that my business process was such that ProductIDs were decided around a conference table and manually entered into the database.

Well I could say then ProductID should be my primary key. One ProductID should always identify a row in this table in this database. Well I have it open in Design. I can right- click the column and just say Set primary key. Notice what happens to the Allow Nulls column when I do this. It's going to turn it off because when you think about it, it doesn't make sense. You can't really have a unique primary key if you're allowing that value to not be entered at all.

So I'm going to hit that and say cool, I'm done. A ProductID will be unique and it will be manually entered in for each product. I'm going to now try and save my changes and the problem that I run into, it will say "Saving changes is not permitted." The changes that I've made require the following table to be dropped and re-created. Now this is one of the problems here, one of the issues. It's why I say that you want to figure your database tables out before you build them, because you don't want to have to go back in and edit them multiple times.

Many of the changes that you might think are just a small change, according to the database are fairly big ones, and in fact SQL Server Management Studio is not letting me save that change. The change it cares about was not actually the primary key. It was me saying that Nulls were allowed and now they're not. Even though I have no data stored in this table yet, it's still considering that a really significant change so it's stopping me from doing it. Well I can tell SQL Server Management Studio to lighten up a little bit. I am going to go to my Tools > Options and find my Designers section where I have an option here that says Prevent saving changes that require table re-creation.

I am going to uncheck that, so I am saying yes, I can save a substantial change that requires the table to be re-created. You want to be careful with that one because obviously un-checking that allows you to make some fairly significant changes that you might not want to. So I'm going to now try that, save again, and we are good. W now have a primary key defined on that column. Well what about the other table? We have dbo.Employee here. I am going to right-click and select Design. I can scan the columns here and see that there is no primary key because you do get it just showing up there if you need to. And I can look at that and think, well, is the one that is obvious? And there isn't.

You could make a case that says well, perhaps first name and last name together could be a primary key, and in fact you can do something like that. It's what's called a compound key, but still in a big company there is no guarantee that you wouldn't get two people with the same first and last name. So here would be a good idea for just creating one. I am going to add an EmployeeID, and this one I'm going to say is just going to be an integer. It's just going to be a number. If we say that every employee has to have one, I'm going to uncheck this and say no, don't allow Nulls. Don't allow that missing value there.

And I could just right-click and name this as the primary key and that would work. However, it does mean that right now I would have to manually type this in or have an application that creates it. What a nice thing would be is can we get SQL Server to help us generate that EmployeeID every time a new employee is added. And not surprisingly, and I know where you think I'm going with this, you can. If I keep this column highlighted so EmployeeID is highlighted and then down in the Properties for the column we have a section called Identity Specification.

This is a little switch that we can flip and it says Is Identity from No to Yes. And then what it changes and it says you've got an Identity Seed and Identity Increment, which is basically what number do we start with and how much do we go up each time. So the default is we start at number 1 and add 1 to it every time around, but I can decide to start it any number. Let's start at 500 and go up by 3 each time around. I'm going to now just save these changes and we now have a primary key defined there.

Well it'd be nice to prove it. I'll go ahead and do that. I'm going to right-click the Employee table and say Edit the Top 200 Rows. That switches me into this editing view. I don't have any data yet, so let's put in our first piece. So the FirstName I'll say that will be Joe, LastName as West. You'll notice that every time I am entering something in I get the exclamation mark and it's telling me that the cell has changed but the change has not been committed to the database. The original data was NULL. I'll just continue on. That sounds all right.

I'll see the Title is a Manager, and the HireDate was the first of February in 2005. BirthDate was the first of January of 1970. Phone number was just a text value. I could put pretty much anything in here. The Status was the bit data type and that really means just expecting a Boolean value, either true or false. A lot of developers wonder should they put a 1 or a 0. Well you can just write the word true in there.

You might think well what happens if I didn't, if I just typed in the number 99? Well as soon as I try and tab off it, it's going to say, "I'm sorry this change value is not recognized as valid." You'd get this on any of these fields. The string was not recognized as a valid Boolean. Okay, that makes sense. I'll click OK and I'll type true, which should be a valid Boolean, and it allow me to tab off. Now you notice here I'm now on EmployeeID. This is the one that should be our identity and should be automatically created.

So I am not going to type anything in here. I am just going to tab, which would make me go to the next row. And when I do that we take off that first row, and by leaving the row all these changes should now be committed to the database, and if I move to the right a little bit I can see that I am actually Employee 500, that it's been entered correctly, and if I would to enter in more information, it will be 503, 506, 509, 512 because we said that the Identity Increment was a factor of 3 for that.

And the last thing I'm going to actually do here is change this EmployeeID and I want to show it first and I can just do that by rearranging my column. I am going to grab it and just drag it up to the top and save my changes. Just going to close these existing windows down right now and reopen the Employee table and I'll just say select the Top 1000 Rows. And what'll happen is it's bringing back that information where EmployeeID 500, all the data that I just entered in, and it does actually show me the command that is really being executed right now, which is just a Select statement.

We'll get into those a lot later. And you'll notice that I do have a Keys folder and I can expand it and it can show me PK_Employee, which means that the primary key for employee has been defined. Now there are different kinds of keys that you can create. You can also create what are called secondary keys, anytime you know you're going to be using a particular field to try and access a part of the database, but we'll talk about those a little later on. Primary keys are what we need to start dealing with first.

Find answers to the most frequently asked questions about SQL Server 2008 Essential Training .

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Q: I'm having problems installing the free Express R2 version of SQL Server on Windows XP. I tried 64-bit and 32-bit versions. In the videos, the author installs from a DVD. Do I need to do the same?
A: While the author installs from a DVD, it's not strictly necessary. There certainly shouldn't be a problem installing the Express edition from a regular download. That's the way it's intended to be installed.

If you're using Windows XP, the only officially supported version is the 32-bit version. However, you do need to make sure that your Windows XP install is completely up-to-date and patched, with XP Service Pack 3 installed. (See http://msdn.microsoft.com/en-us/library/ms143506.aspx#Express32 for formal requirements.)

It's not unusual for the install process to take a while, and with older operating systems like XP, you'll often have to back it out and try again, as usually there's a bunch of prerequisites that need to be installed. (Like the .NET Framework 3.5 SP1, the correct version of Windows Installer, etc.)
Q: The link to the installer for the AdventureWorks sample database, as shown in the Chapter 2 movie "Installing sample databases," no longer works. Where can I find the installer?
A: Microsoft has reorganized its site. The sample files are still there, but they're a bit harder to find. To install them:

1) Visit http://msftdbprodsamples.codeplex.com/.
2) Click the link to "SQL Server 2008 R2 OLTP."
3) Click the AdventureWOkrs2008R2 Data File link and agree to the conditions to download the MDF file.
4) Move the MDF file to your SQL Server Directory, usually located at C:\Program Files\Microsfot SQL Server\MSSQL 10_50.MSSQLSERVER\MSSQL\DATA.
5) Open the SQL Sever Management Studio and connect to your instance using an account with administrative privileges.
6) Attach the sample database by right-clicking the Databases folder in the Object Explorer and choosing Attach from the pop-up menu.
7) Click the Add button in the next menu and navigate to the MDF file in the Locate Database Files window that appears. Select it and click OK.
8) Remove the reference to the log file in the "AdventureWorks2008R2" database details: pane by selecting the Log entry and clicking removing.*
9) Click OK to return to SQL Server Management Studio and complete the attachment process.

*MDF files are the "data" files for SQL Server databases. They often come along with LOG files (ldf files). This one didn't so we need to REMOVE the reference to the non-existent log file. Select the second row in the lower section (it should say File Type: Log and Message: Not Found) and click the REMOVE button.

For an illustrated version of these instructions (with screenshots), click here for a PDF version.
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