@ratchetfreak Yeah, moving/transforming a small amount of data is always better than more, I imagine that holds true at all levels of hardware. What caused me to realize that I didn't have the mental tools to understand querying a db was my coworker explaining how a query he had written got "optimized" by having a certain select reversed. I'd imagine this could be something similar to reading from a linear array backwards vs forwards, thanks to a little game dev experience I know about cache behavior at the cpu end but I have no clue as to what the reasoning is for a db.
If he's talking about "SELECT A B" vs. "SELECT B A" then that shouldn't matter. It may perhaps change some cpu cache behavior but I doubt it's significant when taking into account the surrounding processing.
The only way that could matter significantly is if the query interpreter uses the order of SELECT fields in some way for the execution and frankly I'd say that's a bug.
Not including some columns of a table can have significant impact (when a table is split up internally to separate variable length fields from fixed length fields and you don't SELECT any varchar column.)