What's a good way to check if two datetimes are on the same calendar day in TSQL?

Question

Here is the issue I am having: I have a large query that needs to compare datetimes in the where clause to see if two dates are on the same day. My current solution, which suck

Answer 1

Make sure to read Only In A Database Can You Get 1000% + Improvement By Changing A Few Lines Of Code so that you are sure that the optimizer can utilize the index effectively when messing with dates