This is a really nicely written and illustrated post. An advanced extension to this is that there are algorithms which calculate the number of records to skip

This is a really nicely written and illustrated post. An advanced extension to this is that there are algorithms which calculate the number of records to skip rather than doing a trial per record. This has a good write-up of them: https://richardstartin.github.io/posts/reservoir-sampling https://richardstartin.github.io/posts/reservoir-sampling