How to match a mysql datetime field for a specific day

Sometimes you need a mysql statement to match a datetime field for an entire day.  For instance, if you have an event that has a single start_date field which is datetime, and you want to grab all events for the entire day. 

If your event has start_date field that is type datetime, you can grab all of today's events like so (php code:

$dt = date('Y-m-d',time());

$where = "start_date < '$dt 23:59:59' and start_date > '$dt 00:00:00'";

Just add that $where variable to your where clause when selecting records, and you can get all the appropriate records.