Arnaud Lesauvage <arnaud.listes@codata.eu> writes:
> I am still a bit intrigued by the different query plans. Both query look
> very similar to me, so why does the planner make so different choices ?
Sometime in the future they might generate the same plan. Right now the
planner's ability to optimize sub-SELECTs is pretty limited, and so you
typically get a nestloop-like plan even if some other join style would
be faster. (It's not all the planner's fault either --- we'd need to
tweak the executor so that it could throw the appropriate error for more
than one join partner row, etc.)
regards, tom lane