Unique column constraints in SharePoint 2010

In this article we will be seeing how to enforce unique value for a list or library column in SharePoint 2010.

In SharePoint 2010 we can enforce uniqueness on values in a list or library column, effectively creating a primary key. When you create a column in the list or library you could see an option "Enforce Unique Values" where you can enforce uniqueness. When you enforce uniqueness on a Lookup column, the list item in the target list can have only one list item looking up to it from the child list.

Supported Column Types

• Single line of text
• Choice field (but not multichoice)
• Number
• Currency
• Date/ Time
• Lookup (but not multivalve)
• Person or Group (but not multivalve)
• Title (but not in a document library)

Unsupported Column Types

• Multiple lines of text
• Hyperlink/Picture
• Custom Field Types
• Calculated Field
• Boolean (yes/no)
• Modified by
• Modified time
• UI version
• Created time
• Checked out to
• Content type ID

I have created one list "cl" which has "Title", "TestCol" and "LookUp Col".

When you make Enforce Unique values to "Yes", you will be getting the following pop up.

I have enforced unique values to "Yes" for TestCol (Single Line of text) and LookUp Col.

The items in the list are shown in the following



When I try to add the same value, I was getting the following error



Note: Comparison is case-insensitive, so the values "Test" and "test" are evaluated as equivalent.