There is a lovely little feature in SharePoint 2010 called “enforce unique values”. This prevents users from duplicating data. The option is available any time you create a column.
So when you have a list of companies for example, and you try to capture a new record with an existing company name, you will be stopped.
But! A common action in lists, is to restrict users from editing and viewing other items in that list. You can change the settings so that they can only edit / view their own items. (Found under List Settings – Advanced Settings).
If you try and activate this restriction while you have enforce unique values activated, you will get an error message :
If you read the error, it makes sense. What it is telling you, is that you can’t make users type unique values if they can’t see all the values available to them.
So if you want users to be restricted in what they see, you may get duplicate entries. If you don’t want duplicate entries, then all users must be able to see all the items in the list.
What you can do though, is give everyone read rights to the complete list and edit rights on their own. Then enforcing unique values will work just just fine.
Views from Veronique 
You sound very frustrated. All people working with SharePoint go through this sometimes. Just don’t use the functionality that you don’t like. There’s no law that says you must. 🙂
LikeLike
This design choice is just one of many random design choices by the MS SP team…
If I click enforecing unique values, im telling you not to allow duplicates….. sooo how can I get duplicate data?
Why on earth do the users need to see a list of what is already taken??
when you create an email account do you go through a list of all the taken Email addresses???
No.
it tells you the values was arealy taken and to choose another.. what kind of prodcut is this.. not a business friendly one…
LikeLike
Hello,
Do you know any method to enforce unique value and limit “view and edit” access to users ?
It does make sense for what I’m doing: users post request; I want them to be only able to view there own request et not able to post multiple requests. The unique value would be their email.
Are there any other method to do so?
Thanks and regards
Clement
LikeLike
[…] SharePoint 2010: Enforcing Unique Values and Limiting Access on Custom Lists (Views from Veronique) There is a lovely little feature in SharePoint 2010 called “enforce unique values”. This prevents users from duplicating data. The option is available any time you create a column. So when you have a list of companies for example, and you try to capture a new record with an existing company name, you will be stopped. […]
LikeLike
[…] SharePoint 2010: Enforcing Unique Values and Limiting Access on Custom Lists (Views from Veronique)There is a lovely little feature in SharePoint 2010 called “enforce unique values”. This prevents users from duplicating data. The option is available any time you create a column. So when you have a list of companies for example, and you try to capture a new record with an existing company name, you will be stopped. […]
LikeLike