Try this in your load script:
Code as CostCode ,
Code2 as CostCode , //must be the same name as above
This will add the Descriptors field to your Data based on the CostCode.
Is this what you are looking for?
Dennis's solution will work and also have the benefit of giving all CostCodes and Descriptions even if they are not present in the Charges tables.
Generally though, for this kind of lookup you would use mapping with ApplyMap(). Look it up in the F1 help but in this case you would have the following in your load script:
ApplyMap('Map_CostCodes',CostCode,'<No Description>') AS CC_Description
Hope this helps,