But if we hover over that index seek, we can see in the tooltip that there’s a hidden predicate that is NOT a seek predicate. This is a hidden filter. And because this is SQL Server 2016, we can see “Number of Rows Read” — it had to read 9.3 million rows to count 1.9 million rows. It didn’t realize the 2006 rows were together– it checked all the females and examined the FakeBirthDateStamp column for each row.
Built-in functions can cause SARGability issues.