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


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