Hi Vishal

I don't believe there is currently a way to implement this requirement in smartforms. I understand there is some "For each" rule functionality planned for future releases that may allow you to check for duplicates before committing to the database.

Can I suggest you look at implementing this business logic at the database layer. You could create a stored procedure that checks for any duplicates and map this to the create method for the SmartObject. The downside of this approach is that you can’t check for duplicates before the user commits (i.e. click Save) and therefore you can't notify the user of duplicates, and stop the save, before committing the data.

You could perhaps create a new smartobject method that  saves the list data to a temporary/staging table first when the user clicks save. You could then call another method that performs a duplicate test, and returns a result (e.g. true/false to indicate duplicates) to the smartform to indicate if duplicates are present. If they are present you can stop the actual save (using rule conditions) and alert the user. If they are not present then you can proceed with the save (or call a method to just insert the data from the temporary/staging table into the destination table).

http://community.k2.com/t5/K2-blackpearl/How-to-validate-for-duplicate-row-entry-on-a-list-view/ta-p/86291