Tom Raney <[EMAIL PROTECTED]> writes:
> Why does the planner consider both input variations of each symmetric merge
> join? The README says "there is not a lot of difference" between the two
> options. When are there any differences?
The righthand side needs to support mark/restore, the left doesn't;
so depending on plan types one way might need a helper Materialize
node that the other way doesn't. Also, duplicated values are a bit
cheaper to process on the left than the right.
regards, tom lane
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