Enforcing Uniqueness in Column Values in SharePoint

Supported Column Types
Following is a list of column types that can be indexed and for which unique column constraints are supported:

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

Unsupported Column Types

Following is a list of column types that cannot be indexed and for which unique column constraints are not supported:

• 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