Comment by SahAssar

> Why not write simple SQL queries and use another language to do the transformations?

> Are SQL engines really more efficient at filtering/matching/aggregating data when doing complex queries?

Yes. With knowledge of the data (like indices) and statistics of the data it is usually very much more efficient than piping the data to another process to handle the same job.

Of course that requires you to write a good query and know how to tell what makes a good query, but if your data is in a relational database it is usually more efficient to do your filtering/matching/aggregating there.