If the purpose of the query is to provide data for a report, don't. Let the
report's sorting and grouping options do it. You can group by hours, days,
weeks, months, etc., there.
If you need it for some other reason, use the Fix function to strip out the
time part. Something like:
JustTheDate: Fix([YourDateField])
Of course this will just leave you with a number like 37330. To make it look
like a date again, you can use format or the CDate function.
JustTheDate: Format(Fix([YourDateField]),"Short Date")