I understand that a SET table has an overhead of checking for duplicate rows while data is being inserted into the table. However, if the table has a UPI/USI defined on it, only the UPI/USI columns are checked for duplicates and not duplicate row checks. Is this understanding correct ?

Dear All, 
I have a weird situation, where one my application team asks us to add a column to an existing table, the new column will get populated after 2 months. Until two months they want to keep the values to Null, after which they shall load the data into table which will be unique, they are asking if we can declare this column as USI ? 

Hey guys,

When you have a NUPI, it's good to have a USI because this can enforce uniqueness on your NUPI.

Just wanted to ask for a particular scenario where you will have a combination of NUPI and USI?