I’m trying to write a report which will join a person, their work, and their hourly wage at the time of work. I cannot seem to figure out the best way to join the person’s cost when the date is less than the date of the work.
Let’s say a person cost $30 per hour at the start of the year then got a $10 raise o Feb 5 and another on Mar 1.
- 01/01/2010 $30.00 (per hour)
- 02/05/2010 $40.00
- 03/01/2010 $45.00
The person put in hours several days which span the rasies.
- 01/05/2010 10 hours (should be at $30/hr)
- 01/27/2010 5 hours (again at $30)
- 02/10/2010 10 hours (at $40/hr)
- 03/03/2010 5 hours (at $45/hr)
I’m trying to write one SQL statement which will pull the hours, the cost per hour, and the hours*cost. The cost is the hourly rate last entered into the system so the cost date is less than the work date, ordered by cost date limit 1.
SELECT person.id, person.name, work.hours, person_costs.value,
work.hours * person_costs.value AS value
FROM person
JOIN work ON person.id = work.person_id
JOIN person_costs ON person.id = person_costs.person_id
AND person_costs.date < work.date
WHERE person.id = 1234
ORDER BY work.date ASC
The problem I’m having, the person_costs isn’t ordered by date in descending order. It’s pulling out “any” value (naturally sorted by record position) which matches the condition. How do I select the first person_cost value which is older than the work date?
Thanks!
The best solution is to change the person_costs table so that it records the price over a date interval (start and finish) rather the price after a change. As long as you don’t create any overlapping intervals, the join will always fetch only one row per person/date.
If you can’t change the table structure, you can create a view that achieves the same effect.