MPI, MapReduce, or Spark for complex datasets and processing
If I understand your question correctly. What you want to do is 


Write a sql query against to a database to get the processed/aggregated results first.
Execute several queries in parallel.


The first thing first, if you want to run MapReduce programs on your data, you need to distribute your data. In addition, MapReduce doesn't run your queries to different nodes separately. If your $query_{A}$ runs on $data_{A}$, what we do here is to divide $data_{A}$ to different nodes and run $query_{A}$ on these nodes on $PartOfData_{A}$ in parallel. By the way, you can use Sqoop to migrate the data from your DB to HDFS(it is used to store data separately).

Here are steps for you:


migrate all/part of your data to HDFS
transform your queries to MapReduce version program