comparing times/schedule algorithm

[s3ib]

Hi!

I want to make a TV Guide application. I havent started real coding yet as i am still trying to think through some points of it. I have a question about time handling. User can add new TV channel and if it's added he later can add programs to it. Channels and programs are stored in a different SQL tables(i'm going to use PostgreSQL).
When user try-s to add some new programm to certain channel, I somehow have to determine that there-s nothing allready on, on that time and if there is, it has to send an error to user. Problem is that i don't know how to do it.
It would be easy if the previously stored program would start in exactly the same time as the new program user would to add, then a simple SQL query would do the trick. But that isnt allways the case.
Let's say that user tries to add a show(duration 1 hour) on Channel1 that would start 16:00 at Monday. But there could be allready a show that starts 13:00 and lasts for 7 hours or there could allready be a show that starts 16:30.

My question is what are my options to handle this problem? Should it be done in a database or should it be done in Java. Sure there is a robust way to query all the programs that are on that specific channel on that specific day and then do some math in java but isnt there a cleaner way?
Something like fetch me two programs from db that are closest(1 before, 1 after) to the starting time of the program user likes to add.

One restriction that i have is that TV_program table can have only these fields:
Primary key
Name
Genre
Starting time
Duration
Foreign key of the channel that it's related to.

[delican]

you must design reboust database design and constraints. don't code constraints in java code or use class to gather everything.