How do I speed up complex multi source SQL queries?

The complex pulls take forever partly because you are solving the whole thing in your head at once. A query across many sources is not one giant problem. It is several small ones stacked, and untangling them one layer at a time is what makes it faster. Build in pieces. Get each source returning exactly what you need on its own first, then join. Use small temporary results or common table expressions so you can check each step before combining. When something is slow, look at what you are joining on and whether the columns are indexed. Most of the pain hides in a few bad joins, not the whole query. Next time you face a slow multi-source pull, break it into named steps and run them one at a time. Confirm each is right and quick before stacking the next. You will move slower on paper and much faster in truth, because you stop chasing bugs through a tangle you cannot see.