Database design regarding two 'linking' tables
 

Hi all, im fairly new to database design and would just like a few tips if this is done correctly or if i can improve it..

Im mainly designing a 'leave' application and have an issue with regards to design of two linking tables..

First Table - [Request]
Username, DateStart, DateEnd, DayAmount

Second Table - [Log]
Username, DateStart, DateEnd, DayDate

basically the second table fills in the days of all the dates between the DateStart (starting date) and DateEnd (ending date)..

however im not sure if its good database design to use 3 columns as a primary key and if theres another easier way to solve this issue.

Thanks for your help :)