From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Broersma <richard.broersma@gmail.com>
Cc: sql pgsql <pgsql-sql@postgresql.org>
Subject: Re: Learning about WITH RECURSIVE
Date: Wed, 04 Nov 2009 19:04:01 -0500
Message-ID: <144.1257379441@sss.pgh.pa.us> (raw)
In-Reply-To: <396486430911041427q3a0c9518v9c999a34290798ed@mail.gmail.com>
References: <396486430911041403u639c750bn488ada60822448c0@mail.gmail.com>
<27333.1257372664@sss.pgh.pa.us>
<396486430911041427q3a0c9518v9c999a34290798ed@mail.gmail.com>
Richard Broersma <richard.broersma@gmail.com> writes:
> Actually I'm still confused. I must me missing something. When I
> manually following the directions of:
> http://www.postgresql.org/docs/8.4/interactive/queries-with.html> I get the following when I try:
> WITH RECURSIVE t(n) AS (
> VALUES (1)
> UNION ALL
> SELECT n+1 FROM t WHERE n < 100
> )
> SELECT sum(n) FROM t;
> (1) --initial non-recursive working table
> (1) UA (2) = (1,2) --new(1) working table
> (1,2) UA (2,3) = (1,2,2,3) --new(2) working table
> (1,2,2,3) UA (2,3,3,4) = (1,2,2,2,3,3,3,4) --new(3) working table
You're confusing the working table with the final output. In this
test case, the working table contains exactly one row after each
step (except after the last, when it contains no rows). That one
row is also added to the result, but we don't use the whole result
for the next iteration of the recursive term.
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, richard.broersma@gmail.com
Subject: Re: Learning about WITH RECURSIVE
In-Reply-To: <144.1257379441@sss.pgh.pa.us>
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