Erik Darling answers an office hours question in detail. The question comes down to why a filter on ROW_NUMBER() where the row number is equal to 1 could differ from the same query where row number is less than or equal to 1. Knowing that ROW_NUMBER() starts at 1 and can never be anything other than a natural number, you’d think that SQL Server would treat these exactly the same. But Erik shows an example where the two can differ, and the answer was a good one. I will admit that my pre-video guess was wrong but once he showed the execution plans, things clicked. And, like Erik mentions, this is why it’s so important to dig into the execution plan, because the answers are typically in there somewhere.