Query related to Hadoop's map-reduce

Scenario:

I have one subset of database and one dataware house. I have bring this both things on HDFS. I want to analyse the result based on subset and datawarehouse. (In short, for one record in subset I have to scan each and every record in dataware house).

Question:

I want to do this task using Map-Reduce algo. I am not getting that how to take both files as a input in mapper and also how to handle both files in map phase of map-reduce.

Pls suggest me some idea so that I can able to perform it?