[switch007]

> Fact: If you just downvote me without explaining why, neither of us can learn anything.

Didn't downvote you but your first comment I found vacuous. "Possibly", "could pump", "I was informed...I've no experience of it".

Your second comment then asserts things which may very well be true, but would be more believable with some references.

[tempguy9999]

Thank you for a helpful comment. I can see the initial comment wasn't sufficient now you've explained how it looks to you.

The 2nd post is harder to justify in a way. Some of it comes from experience, and understanding the behaviour of a merge join vs a loop join for example, and how much slower the latter can be if applied wrongly, which points to why the optimiser is so vital.

Edit: there's also the cardinality estimation (which can so easily go wrong), the dynamic programming for joins and the combinatorial explosion when it comes to ordering/reordering of inner joins, heuristic costs of using indexes vs not, etc.

Some of it was hearsay, but I stated it as such. Anyway, point taken, and thanks again.