Re: Change JOIN tutorial to focus more on explicit joins

From: Jürgen Purtz <juergen(at)purtz(dot)de>
To: "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>
Cc: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Thomas Kellerer <shammat(at)gmx(dot)net>, Pg Docs <pgsql-docs(at)lists(dot)postgresql(dot)org>
Subject: Re: Change JOIN tutorial to focus more on explicit joins
Date: 2020-10-22 13:32:00
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On 22.10.20 01:40, David G. Johnston wrote:
> On Fri, Sep 4, 2020 at 2:36 AM Jürgen Purtz <juergen(at)purtz(dot)de
> <mailto:juergen(at)purtz(dot)de>> wrote:
> On 04.09.20 08:52, Peter Eisentraut wrote:
> >
> > For the remaining patch I have a couple of concerns:
> This patch should not be changing the formatting choices for these
> queries, just the addition of a JOIN clause and modification of the
> WHERE clause.  Specifically, SELECT is left-aligned while all
> subsequent clauses indent under it.  Forced alignment by adding extra
> spaces isn't done here either.  I have not altered those in the attached.
> Did some word-smithing on the first paragraph.  The part about the
> cross-join was hurt by "in some way" and "may be" is not needed.
> Pointing out that values from both tables doesn't seem like an
> improvement when the second item covers that and it is more specific
> in noting that the city name that is joined on appears twice - once
> from each table.
> ON expression is more precise and the reader should be ok with the term.
> Removal of the exercise is good.  Not the time to discuss cross join
> anyway.  Given that "ON true" works the cross join form isn't even
> required.
> In the FROM clause form I would not add table prefixes to the column
> names.  They are not part of the form changing.  If discussion about
> table prefixing is desired it should be done explicitly and by
> itself.  They are used later on, I didn't check to see whether that
> was covered or might be confusing.
> I suggested a wording for why to use join syntax that doesn't involve
> legacy and points out its merit compared to sticking a join expression
> into the where clause.
> The original patch missed having the syntax for the first left outer
> join conform to the multi-line query writing standard you introduced. 
> I did not change.
> The "AND" ON clause should just go with (not changed):
> ON (w1.temp_lo < w2.temp_lo
>     AND w1.temp_hi > w2.temp_high);
> Attaching my suggestions made on top of the attached original
> 0002-query.patch
> David J.
(Hopefully) I have integrated all of David's suggestions as well as the
following rules:

- Syntax formatting with the previously used 4 spaces plus newline for JOIN

- Table aliases only when necessary or explicitly discussed

The discussion about the explicit vs. implicit syntax is added to the
"As join expressions serve a specific purpose ... " sentence and creates
a paragraph of its own.

The patch is build on top of master.


J. Purtz

Attachment Content-Type Size
0003-query.patch text/x-patch 6.6 KB

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