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From: Tom Lane <tgl@sss.pgh.pa.us>
To: David G. Johnston <david.g.johnston@gmail.com>
Cc: oselemg@gmail.com
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: Typo on tutorial window page
Date: Tue, 21 Jan 2025 13:10:14 -0500
Message-ID: <3363256.1737483014@sss.pgh.pa.us> (raw)
In-Reply-To: <CAKFQuwaYf8E5oB0t5VCAJZHeJ01XjWH0JKVhASruhSaBNiMOSA@mail.gmail.com>
References: <173737973383.1070.1832752929070067441@wrigleys.postgresql.org>
	<3359764.1737481165@sss.pgh.pa.us>
	<CAKFQuwaYf8E5oB0t5VCAJZHeJ01XjWH0JKVhASruhSaBNiMOSA@mail.gmail.com>

"David G. Johnston" <david.g.johnston@gmail.com> writes:
> I was going to write basically that but something feels off to me.  Maybe
> something like this:

> "As shown here, the rank function produces a numerical ranking within each
> partition, using the order defined by the ORDER BY clause.  Ranking assigns
> the same rank to all rows that tie according to the order by criteria,
> while still incrementing the rank counter.  Thus there are gaps in the
> serial numbering.  These can be removed by instead using the dense_rank
> window function.  Ties can instead be given their own unique value by using
> the row_number window function.  In all these cases, as the window function
> is effectively just counting rows, the function itself has no input
> parameter."

> If we don't want to get into that level of nuance in the tutorial I suggest
> we use the row_number() window function instead of rank, and just say
> because we count rows no parameter is needed.

Yeah, I was wondering if it'd be worth bringing up dense_rank,
but decided "probably not".  I like your idea of switching the
example to use row_number to simplify things.  What would the
text be then?  Perhaps

    As shown here, the <function>row_number</function> function
    assigns sequential numbers to the rows within each partition,
    in the order defined by the <literal>ORDER BY</literal> clause
    (with tied rows numbered in an unspecified order).
    <function>row_number</function> needs no explicit parameter,
    because its behavior
    is entirely determined by the <literal>OVER</literal> clause.

			regards, tom lane

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