Thank you very much for your reply:) Can you please explain me what derby developpers mean exactly with "repeatable table functions" and "read once Streams" ?
Many thanks in advance. Knut Anders Hatlen wrote: > > Reda134 <[EMAIL PROTECTED]> writes: > >> Hi all, >> The Derby devoloppers mentions in the documentation of table functions, >> that >> the optimizer takes 2 Assumtions : >> >> 1 - It Assumes by default that table functions are repeatable and thus >> place >> them in the inner slot of a join. >> >> 2 - It Assumes by default that table functions are expensice and thus >> place >> them in the outer slot of a join. >> >> Is this not paradoxal ?? Or i get it wrong ?? > > I assume you're talking about this section of the developer's guide: > http://db.apache.org/derby/docs/10.4/devguide/cdevspecialtfoptimizer.html > > The clue here is that it doesn't say "thus place them in the > [outer/inner] slot", but rather that it is _likely_ that the optimizer > will place the table function in an outer slot and that the optimizer > _can_ place it in an inner slot. If you for example join two table > functions, only one of them can be in the outer slot. The other one will > go in the inner slot. If none of them can go in the inner slot because > they are not repeatable, one of them will be stored in a temporary table > which can go in the inner slot. > > -- > Knut Anders > > -- View this message in context: http://www.nabble.com/Derby-optimizer-for-Table-Function-tp20456636p20458631.html Sent from the Apache Derby Users mailing list archive at Nabble.com.
