在sql中比较时间(或日期)的最佳方法是什么?

I need two comparisons in my Sql server, One between Dates and One between Times. I'm using C# and Sql Server and Linq-to-sql. I want to store two time fields (Enter-Time, Exit-Time). Now I want to get the difference (e.g. 12:30 , 18:15 the difference is 5:45). What Data Type should I use? I have the same issue with Dates, I want to get the difference of two Dates but "DateTime" Data Type stores redundant data about time, I just need date. I want the easiest way with the least code possible. I'm currently saving like this "1045" when I fetch it I add a ":" to the middle and it becomes "10:45" and there are lot's of problems this way.I need two comparisons in my Sql server, One be