i have a 10+year old project on mysql doing 6+ way joins, groups, etc against 100million row tables in sub second time. It all depends on the indexing, disk lay

i have a 10+year old project on mysql doing 6+ way joins, groups, etc against 100million row tables in sub second time. It all depends on the indexing, disk layout and size of intermediate products etc. We dont know why they did "UNION ALL" with huge intermediate products (it seems like the query could be a single index/table scan on its face) but that is likely the slow down "EXPLAIN SELECT" would tell us