merging tables on two columns

Hi there, 

First post, so apologies if this is super dumb - I was either searching for the wrong thing or being exceedingly dense in understanding what others had written! I have a large (1m row) data table and a small (few hundred row) configuration table and I am trying to merge them together, thus:

Table.Data

Date Monthly Production Unit

etc

Table.Configuration

Date Unit Type1Jobs Type2Jobs

In other words, for the month of Jan, CNC1 did 50% of Type1 jobs and 50% of type 2 jobs, and then in Feb was re-configured to do 60% type 1 jobs and 40% type 2 jobs.

The outcome I want is effectively:

Date Monthly Production Unit Type1Work Type2Work

So the monthly production is shared out based on the fraction of the type of work, per machine. The end result I want to see is type of work over time per machine, as those get grouped by site.

Now, I can do a simple left outer join to achieve a baseline configuration, but I cannot do a join on two columns without getting into between/range type thinking and that is beyond my brain at this time, and therefore any configuration change of the machine is lost.

I see answers sort of suggesting a 2nd date table somehow, but I am struggling to see the solution. I am sure this is super simple, what am I missing?