Enforcing Unique Values in Columns
Certain column types offer the option to Enforce Unique Values for the column. This is a capability that has been requested by many clients over the years, and various workarounds were developed using workflows or leveraging the ID value of the list item. For example, a list that tracks serial numbers, employee IDs, invoices, or many other values will be less valuable if data entry errors can lead to nonunique numbers.
Table 22.1 summarizes what column types can and cannot be used to create unique columns.
Table 22.1. Unique Column Options
Caution
If Content Approval is enabled for a document library and then ...
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