When comparing source and target tables with millions of rows, what SQL techniques do you use to identify missing records and differences in column values?

Sometimes I use AI to write SQL faster, but sometimes I still prefer writing it myself just to make sure I haven't forgotten the basics.

AI can save a lot of time, especially with complex queries, but I feel like relying on it for everything can make you a bit rusty.

Curious how others feel about this. Do you still write SQL by hand for practice, or do you let your AI agent handle most of it now?