Hi all, So I was thinking about the following, after experimenting with constraint exclusion. I thought I would see what happens when I do this: SELECT * FROM ONLY table_a UNION SELECT * FROM table_b; I noticed that despite table_a still having no data in it, the planner has already decided that it needs to insert a chain of ‘append->sort->unique’ nodes into the plan. That’s fairly reasonable. While I understand that we can’t readily know about wether a given node will return anything or not - would it be possible to have the execution engine branch off in the event that a given node returns nothing at all? I guess there are probably a lot of considerations, and I suspect it would considerably increase planning time, though maybe it also presents an opportunity for some interesting approaches to adaptive query execution. I don’t know so much about this, though I’m sure there are all kinds of research papers discussing it. Is this something that has been considered before? Tim |
