title: Why does this sql query do a key lookup?
body: <p>I have a table User with a bunch of indexes. One of them is a unique index on the AccountIdentifier column.</p>
  
  <p>Since this is a unique index, why is a key lookup required in addition to the index seek? The index seek tooltip reports that only one record is returned. I've also tried converting the index to a "unique key" type.</p>
  
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