I agree, they're both right. I've been doing data science since around 2008 and it's a balance between local needs and repeated analysis and an often more effi

I agree, they're both right. I've been doing data science since around 2008 and it's a balance between local needs and repeated analysis and an often more efficient one off query. Sure the SQL optimizer is going to read off the index for a count(*), but it doesn't really help if I need all the rows locally for data mining anyway. The counts need to line up! So I'll take the snapshot of the data locally for the one off analysis and call it a day. If I need this type of report to be run nightly, it will be off of the data warehouse infrastructure not the production DB server. Shrug. These things take type and experience to fully internalize and appreciate.