Validation Settings in SharePoint 2010
Validation settings are new to SharePoint 2010, as is validation for columns. Validation is a formula or statement that must evaluate to TRUE before the data can be saved. The difference between the two is that column validation compares only the data in that single column to some test, such as
= [Discount] < = .50
This means that the discount entered must be less than 50 percent.
Validation settings in the library/list level compare two or more columns to evaluate to TRUE. So you can set a rule that [Discount] < [Cost] so customers don’t get an item for free (or money back!) because they buy an item with a discount.
To use Validation settings, follow these steps:
Click the Validation Settings link in the Library/List Settings page.
The Validation Settings page has two sections, Formula and User Message. The Formula section is the test your comparison of the columns must pass for the item to be valid. The User Message section is what the user receives if the test fails. Users can then adjust their values until the test passes.
Create a formula for the validation by entering it in the Formula field.
The formula needs to compare (or validate) two columns in your library or list. The Library (or List) Settings page provides an example and a link to learning more about the proper syntax.
A selection list of columns in your library/list is available for use in your formula.
In the User Message text box, enter a message to be shown to users who enter an invalid list item.
Click OK or Cancel.
If you click OK, your validation is applied to your list.
Validations aren't retroactive. They apply only to new and modified entries on the specified columns.