I have a situation where a mapping table contains multiple values that
are the same, i.e

1 - a
2 - b
3 - a
1 - d

So in this case, there are multiple possible values for '1'.

I can parse the map table and set this into a nodeset no problems. I can
then loop through this and work on each current-node.

The issue i have is that the map table actually looks like

1 - a - ab
2 - b - bc
3 - a - cd
1 - d - ef

So what I need to do is work through the map table and if the following
conditions are met, return the value

if 1 and a, then return ab
if 1 and d, then return ef

The issue I can see is that the map table only allows you to search on
one condition (Source Column). What I really need is a way to match two
conditions in the map table to return the third value.