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SQL Server 2008 Essential Training
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Creating unique constraints


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SQL Server 2008 Essential Training

with Simon Allardice

Video: Creating unique constraints

Another kind of constraint you can work with is what's called a unique constraint. Now in fact, we already have one of these on most of our tables. If you have a primary key, you have a unique constraint. That primary key cannot be duplicated. In this case, there can only be one ProductID with 1008 in it. But occasionally, you will want to define another column as being a unique constraint, that the value cannot occur more than once in the entirety of the column in that table.
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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. Joining multiple tables together
      8m 0s
    9. Using subqueries
      9m 33s
    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
      31s

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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
Subjects:
Business Developer Servers Databases
Software:
SQL Server
Author:
Simon Allardice

Creating unique constraints

Another kind of constraint you can work with is what's called a unique constraint. Now in fact, we already have one of these on most of our tables. If you have a primary key, you have a unique constraint. That primary key cannot be duplicated. In this case, there can only be one ProductID with 1008 in it. But occasionally, you will want to define another column as being a unique constraint, that the value cannot occur more than once in the entirety of the column in that table.

Now right now none of these columns should be made unique. Certainly not UnitsInStock and certainly not Color. That repeats quite a lot. We might have ProductName made unique, but not the way that we work with it. For example, I have a Road-650 58 in Black and I have a Road-650 58 product in Red and a Road-650 58 product in Green. I can't make ProductName unique. What would be interesting, however, is if I could force uniqueness on a combination of the two.

What that allows me to do is make sure that they aren't accidentally two rows that represent the same product color combination, that the database would not allow me to enter that. Everything we do in our database design should all be about enforcing valid data. So how do we do this? Well, not surprisingly, it's going to be in the Design view of the product. I'm going to right-click that table and jump into Design. Now you won't find any on the unique options in your Column Properties. What you have to do is right-click in the blank designer area and while we had things like Check Constraints there, you don't see a unique constraint.

The area that we are interested in is this one, Indexes/Keys. If I select that, we should find we already have one. Here's my index for the primary key. It's saying this is the ProductID. It is unique, yes, and it is the primary key. We don't want to mess with that. What I want to do is add another one. It's not a primary key. It's what's called a unique key. I am going to click Add and we get this IX_Product, because this dialog box that I'm looking at is how we add new indexes to our table.

How we add new ways of looking things up quicker when we have large amounts of data. Now, we are going to be talking about indexes a little later on. So don't worry too much about all the options here like Create As Clustered and all that stuff. I actually want to change this. I click the Add button and I want to say no, this is not an index. This is a unique key. It changes the Is Unique to Yes. We do have to pick the columns that we are interested in. It's defaulted to ProductID, but ProductID is already unique. I am going to click the little ellipsis button. I am going to say what I actually want is for my column to be ProductName.

And because it's going to create its own little set of product names to make sure that there won't be a duplicate one, we can choose whether that Ascending or Descending. It doesn't matter here. However, I don't want it to be just ProductName. That wouldn't work. In fact, I couldn't enforce that rule on my existing table. It's going to be ProductName and I am going to click beneath it and say Color. That's fine. Color Ascending, ProductName Ascending. I click OK. It's now telling me that the combination is both of them, ProductName and Color. I can ignore the rest of the stuff and just click Close.

This still is considered an unsafe change to my table. So I'm going to save the change now. I am going to go back into editing that and I'm going to add a new product. Let's say in this case it's going to be Road-660 60 in Black and there's 3 UnitsInStock and that works just fine. Now let's say we add Road-650 58 in Green.

Now this one already exists. So when I tab off, I should get a problem. "I'm sorry, there was a Violation of UNIQUE KEY constraint, can't insert duplicate key. The statement has been terminated." Again, if you are a developer, a lot of the times developers think, "Well, surely, I could just take care of that in my application. I'll make a check beforehand." But the great thing about doing it here is we are saving those rules as business rules in the database. We are making sure that we'll never get that duplicate data entered in rather than just trusting an application or a user to make that check for us.

I won't be able to save that. So I can either add it as a new color, Blue, which would allow me to save that row, or I could have deleted that row.

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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