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Creating default values

From: SQL Server 2008 Essential Training

Video: Creating default values

When you're designing databases, it's a good idea to apply as many rules or constraints to your data as possible. And one of the classic ways to do this is by setting up default values for your columns. The idea of this of course is simple. We have a table such as an OrderItem table made of product IDs and quantities and unit prices. Whereas a lot of this information is very different from row to row, Quantity for example might typically be the number 1. Occasionally it might be 2, but nine times out of ten or nineteen times out of twenty or ninety-nine out of a hundred it will be the number 1.

Creating default values

When you're designing databases, it's a good idea to apply as many rules or constraints to your data as possible. And one of the classic ways to do this is by setting up default values for your columns. The idea of this of course is simple. We have a table such as an OrderItem table made of product IDs and quantities and unit prices. Whereas a lot of this information is very different from row to row, Quantity for example might typically be the number 1. Occasionally it might be 2, but nine times out of ten or nineteen times out of twenty or ninety-nine out of a hundred it will be the number 1.

So we will make this the default value for that column, so it doesn't always have to be entered, either by the application or by the user. I'm going to go into my OrderItem table in SQL Server Management Studio and select Design. Applying a default value is very simple. Find the column that you're looking for, in this case Quantity, and then down here in the Column Property section, you'll find a section that says Default Value. We hit the number 1. That's counted as a change to the database definition.

So you'll see that we have the asterisk up here. I am going to hit Save to save those changes to the table. Close that down and now let's test it. I am going to right-click and say Edit Top 200 Rows and I am going to enter in a new order item. I am, of course, just going to do this manually. Now, right now I have OrderItemID added as an identity column for a primary key, which means it will generate that too. Hopefully, the number 19 or the number 20. I am going to put in ProductID-123. I'm going to Tab to skip over the Quantity and I am going to say the UnitPrice is 54.98.

Then I am going to tab off on to next row. Now you will quite often see this message where the row itself kind of shows up in a pale color and the exclamation mark, if I tooltip over it, it will say, "This row was successfully committed to the database. However, there was an issue with retrieving the data back after the commit, because the displayed data is read-only." But it almost certainly worked. So I'm going to just come out of this and go back in and just select the Top 1000 Rows again, just to double check that.

I can see that yes, at position 19 we have ProductID 123 with a default value of 1 at 54.98. Now bear in mind though that the only real point of working with the default value is it will have an effect when a row is being added to the table. If I was editing rows and I just decided, for example, to leave a blank value, it's not going to dump in a new default value for a row that already exists. So I will hit Escape there.

The only place where default values can have an effect after the fact is when we're adding a new column. Let's say going back into OrderItem. I am going top hit Design and I am going to add a new column here that I will call DateCreated. I want this to always have a date or indeed a datetime. I will use datetime2 and uncheck Allow Nulls. I always want a value in this column of when that row was created. When I make that change, if I'm trying to save my changes back, I'm going to get this Post-Save Notification pop-up.

It was unable to modify the table. It gives me a long-winded explanation that really comes down to you can't create a column and say it's not allowed to have null values and then add it to lots of existing rows with null values. Well, one of the ways we can use the default value here is I'm going to say the default value is getdate. This is the default value of DateCreated. If I now save this, what will happen is it's going to use that rule for any new row.

Because we've also used it for pushing a change to this table, it's going to use that value for the old rows as well. Just to close down my existing information, I will then right-click and reopen it up. And I can actually see that the DateCreated has been filled out for all those old rows. From this point forward if I add a new row, ProductID 456, I will skip over Quantity because that should give me a default value. I will do a UnitPrice of 98 and I will skip over the DateCreated.

If we then close that down and just reopen it, I'm going to see that I have both the default value of 1 and the DateCreated of just a moment ago.

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This video is part of

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SQL Server 2008 Essential Training

74 video lessons · 36177 viewers

Simon Allardice
Author

 
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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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