Re: Proposing WITH ITERATIVE
От | Fabien COELHO |
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Тема | Re: Proposing WITH ITERATIVE |
Дата | |
Msg-id | alpine.DEB.2.22.394.2004290648190.978556@pseudo обсуждение исходный текст |
Ответ на | Re: Proposing WITH ITERATIVE ("Jonah H. Harris" <jonah.harris@gmail.com>) |
Ответы |
Re: Proposing WITH ITERATIVE
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Список | pgsql-hackers |
Hello Jonah, Nice. > -- No ORDER/LIMIT is required with ITERATIVE as only a single tuple is > present > EXPLAIN ANALYZE > WITH ITERATIVE fib_sum (iteration, previous_number, new_number) > AS (SELECT 1, 0::numeric, 1::numeric > UNION ALL > SELECT (iteration + 1), new_number, (previous_number + new_number) > FROM fib_sum > WHERE iteration <= 10000) > SELECT r.iteration, r.new_number > FROM fib_sum r; Nice. My 0,02€ about the feature design: I'm wondering about how to use such a feature in the context of WITH query with several queries having different behaviors. Currently "WITH" introduces a named-query (like a view), "WITH RECURSIVE" introduces a mix of recursive and named queries, pg really sees whether each one is recursive or not, and "RECURSIVE" is required but could just be guessed. Now that there could be 3 variants in the mix, and for the feature to be orthogonal I think that it should be allowed. However, there is no obvious way to distinguish a RECURSIVE from an ITERATIVE, as it is more a behavioral thing than a structural one. This suggests allowing to tag each query somehow, eg before, which would be closer to the current approach: WITH foo(i) AS (simple select), RECURSIVE bla(i) AS (recursive select), ITERATIVE blup(i) AS (iterative select), or maybe after AS, which may be clearer because closer to the actual query, which looks better to me: WITH foo(i) AS (simple select), bla(i) AS RECURSIVE (recursive select), boo(i) AS ITERATIVE (iterative select), … Also, with 3 cases I would prefer that the default has a name so someone can talk about it otherwise than saying "default". Maybe SIMPLE would suffice, or something else. ISTM that as nothing is expected between AS and the open parenthesis, there is no need to have a reserved keyword, which is a good thing for the parser. -- Fabien.
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