In SQL there are three basic time types.
timestamp, date, and interval.
Timestamps mark a point on a timeline down to the seconds or milliseconds. They include a date and a time. They can often be entered in more than one format, depending on your database. One common way is like this: '2005-12-29 17:34:11.923844'
A Date is just that, a date, with no time component. They also can be entered in multiple formats, but again, '2005-02-23' is the standard across borders, whereas something like 12/09/2005 might mean December 9th, or September 12th, depending on if you're in Europe or America.
Intervals represent the time between two arbitrary points in time. They are measured in days and seconds. They look like this: '12 days 3 hours 15 minutes 12 seconds' or '12 03:15:12'
for what you're doing, if you have a timestamp with a date attached, you'd do it:
select * from sometable where datefield between '2005-12-29 17:00:00' and '2005-12-31 17:00:00'
If they're intervals, you can use the same basic query with the between / and method.
