I've understood it to be a bit more nuanced than that. If you were to perform two queries: Query 1 -> join Table A with Table B, both have 1M records Query 2

I've understood it to be a bit more nuanced than that. If you were to perform two queries: Query 1 -> join Table A with Table B, both have 1M records Query 2 -> Filter Table A to 10k records, then join Table A with Table B (1M records) I would expect Query 2 to execute faster - I don't think the exec plan would've optimized Query 1 equivalently.