Question

I have two tables

Operators table

proportion, name, routeid

(proportion hold % value e.g 100 = 100% or 50 = 50% this shows the % of services ran by this operator)

route table

routeid, frequency 

(frequency holds number of trains per hour)

What I need to do now is write a query which will sum up the number of trains per hour by certain operator where name of operator is Arriva. So if arriva runs 100% of certain service 1, and 50% of service 2 it should work that out as well.

What I was thinking it would look something like this psudo code

All arriva trains per hour = Frequency * (proportion/100)
Where Operators.name = Arriva

Answer 1

Try this

  select SUM((ot.frequency * rt.proportion)/100.0 )
  from operators_table ot 
    join route_table rt on ot.route_id = rt.route_id
  WHERE ot.name = 'Arriva';