Ensure Uniqueness of Nullable Columns

A couple of weeks ago I encountered a tweet in which one of the questions expected from a candidates in a job interview was the reason to write this post, How do you ensure that duplicate keys are prevented on a column that allows NULL values?

That reminds me of the time that I was focused on databases and I had to handle such problem for one of our databases, here we are going to talk about two approaches to address this issue in SQL Server.

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