I'm not sure what it is today - I would hope the same mindset applies, but maybe not - but back when I was using SQL, the idea was to let the database engine do

I'm not sure what it is today - I would hope the same mindset applies, but maybe not - but back when I was using SQL, the idea was to let the database engine do everything it could with the data, before sending the results over the pipe. That is, minimize the network bandwidth by putting the work on the DB engine. This of course necessitated creating and understanding proper SQL query building practices. It was real easy to mess up if you didn't know what you were doing (ie - inner selects, improper joins, etc) and cause a combinatorial explosion that would consume all the RAM on the server and grind it to a halt. That, or bring back a load of data that you then filtered on the "client" - better to let the DB server do that if you can. Of course, this was back when the clients were 486s and early Pentiums with maybe 8-16 MB RAM. Today it's a bit different, but you still want to minimize the network traffic.