Question

I have the following tables (simplified):

   hours               hour_rates
 - user_id            - user_id
 - date               - date
 - hours              - hourly_rate

Hours table example:

1 - 2012-03-19 - 8

This means that user with id=1, at 2012-03-19 worked 8 hours in total.

The hourly rate for a person can change in time, so I have the second table:

hour_rates table Example

1 - 2011-12-01 - 20
1 - 2011-12-20 - 25

So for user with id=1, we set a hourly rate of 20$ at 2011-12-01.
We changed his hourly rate at 2011-12-20, to 25$.

What I want is, to calculate how much I have to pay for a given user (ex. id=1) for a given period (ex. 2012-01-01 -> 2012-02-01).

Can I calculate this simply mysql side?
If not, how to do it in an efficient way?

Answer 1

In hour_rates table you should have two dates: start_date and end_date this means from start_date to end_date the emplyer has been paid x$ per hour.

Then use the same query proposed by bpgergo modified like this:

   select sum(h.hours * hr.hourly_rate) as pay
   from hours h, hour_rates hr
   where h.user_id = :user_id --here you will set the user id parameter
   and h.user_id = hr.user_id and (h.date BETWEEN hr.start_date AND hr.end_date 
   and h.date between STR_TO_DATE('01,1,2012','%d,%m,%Y') and STR_TO_DATE('01,1,2011','%d,%m,%Y')