Re: Change JOIN tutorial to focus more on explicit joins

On 22.10.20 01:40, David G. Johnston wrote:
> On Fri, Sep 4, 2020 at 2:36 AM Jürgen Purtz <juergen@purtz.de 
> <mailto:juergen@purtz.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