I want to compare date type value with dateTime type value ,how is it possible?

You can cast a datetime into a date using todate().

The exact answer really kinda depends on what you hope to accomplish.  How will a bare date be treated in comparison with a datetime?  If someone compares today's date versus today's date at 2 PM, for instance, should the comparison return tha they're equal, or that the value that's 14 hours after midnight be greater?  Or some other behavior?