Date compare in scheduling emplooyee job

Hello.

The situation example in this: 

Our company has 100 employees. We assign some employees to do job in several days. A and B and C given job in Oktober 5 to Oktober 9, and it is inputted and recorded in the system.
So if someone input A and B to do another job in October 8 to October 10,, the system will reject and gives warning that A and B already have the job in Oktober 5 to Oktober 9. 
Is there any CI function that deal with date to avoid problem like that ? Date comparison? Date between in? What logic to solve that problem?

I use CI 3 and mysql.

Thank you.