i have an issue with start date and end date?

It's about a resort where customer can book the room with start and end time mentioning.

for example: if ravi booked room no 106 from 2015-5-05 to 2015-5-20 and if rahul tries to book the same room from 2015-5-12 to 2015-5-17 .It should report a messagge but in my case the room is booked for rahul from 21-26(since the earlier days are booked already.)

I have to know how to compare the in between dates while insertion using mysql in php