So let’s check. The picture above shows, side by side, the properties of the Index Seek and the Key Lookup operator. They show that the Index Seek did 3 logical reads only, while Key Lookup did 650 logical reads. A clear indication where the majority of the work is done.
But wait. Aren’t we missing something?
SET STATISTICS IO ONoutput indicates a total of 722 logical reads. The two screenshots above add up to 653 logical reads. Where are the other 69 logical reads?
Read on for the answer.