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Creating check constraints

From: SQL Server 2008 Essential Training

Video: Creating check constraints

Another way that we can increase the reliability, the integrity of our data, is to apply what are called check constraints. A check constraint is a simple idea. If we have some data such as Quantity where we can look at that and understand this really unacceptable range for this to be in, even though this column is actually being defined as an int, we don't need all that an int can give us. Because an integer can support from roughly -2 billion to plus 2 billion, it is quite unlikely that someone will order -2 billion quantities of a unit.

Creating check constraints

Another way that we can increase the reliability, the integrity of our data, is to apply what are called check constraints. A check constraint is a simple idea. If we have some data such as Quantity where we can look at that and understand this really unacceptable range for this to be in, even though this column is actually being defined as an int, we don't need all that an int can give us. Because an integer can support from roughly -2 billion to plus 2 billion, it is quite unlikely that someone will order -2 billion quantities of a unit.

So let's say I want to enforce some rules on this column that says Quantity must be greater than 0 and less than 51 say. Well, I do this by applying a check constraint to the table. I am going to right-click anywhere in the Designer area. It really doesn't matter. And I have a section called Check Constraints. Right now it's saying there are no check constraints on this table. I am going to add one. It's typically called CK_ the name of the table. What we need to type in is an expression. In this case, it's quite simple. Quantity > 0 AND Quantity < 51. Close.

We now have a check constraint defined on the table. It is considered a table change. So I see the asterisk. I have got to save that. Close this down. Now, when I go into that table and I say change one of the existing rows, 50 is accepted as a change and I can click off that row. 51 will actually throw an error here. The update statement conflicted with the check constraint. I also can't put a 0 Quantity and I can't put a negative Quantity.

Check constraints can easily be removed. I need to escape out of here before it tries to apply those changes. I could go back into the Design view, again right-clicking anywhere in the Designer, because the check constraints are defined for the table. They're not defined specifically on a column. It's just this expression. You could have one check constraint that has multiple columns in it. Quantity above a certain amount if ProductID in a particular range. But if we wanted to, we could just come in here and hit the Delete button to remove the check constraint from the table, but I'm going to keep it.

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This video is part of

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SQL Server 2008 Essential Training

74 video lessons · 35825 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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