That's completely backwards. Mapreduce-like approaches are how SQL datastores are implemented underneath; the absolute best case for SQL is to equal hand-tuned mapreduce-like performance, and often it will be slower (you're at the mercy of your query planner to pick the right indices, do joins in the right order, etc.). The main reason people use SQL is because they find it easier to express a query that way (which is completely legitimate - if your query planner is good enough most of the time, you've got better things to be doing than hand-tuning your query execution).