I found claude sonnet 4 really good at writing SQL if you give it a feedback loop with real data. It will research the problem, research the data, and improve queries until it finds a solution. And then it will optimize it, even optimize performance if you ask it to run explain plan or look at pg_stat_statemnts (postgres).
It's outrageously good at performance optimization. There's been multiple really complex queries I've optimized with it that I'd been putting off for a long time. Claude code figured the exact indexes to add within seconds (not ones I would have got easily manually).
