SQL to select only certain times within a date range

This is one of the few times where having separate DATE and TIME columns would be beneficial.

select columns
  from table
 where datecol between '2007-07-01' and '2007-07-31'
   and (
       timecol >= '22:00'
    or timecol <= '06:00'
       )

With a DATETIME column, however, it's a little trickier. We need to "extract" the time portion of the DATETIME values. The query would look something like this:

select columns
  from table
 where datetimecol >= '2007-07-01' 
   and datetimecol  < '2007-08-01'
   and (
       extract(hour from datetimecol) >= 22
    or extract(hour_minute from datetimecol) <= '06:00'
       )

Exact syntax will depend on which database system you're using. Notice how the range test for the dates uses an open-ended interval.