Re: Speaking of SQL.....

IMO, using UNION can simplify debugging somewhat, even when you're working
with one table and a very complex set of WHERE's. And you can add a
literal to each Select statement to identify the table/the WHERE's from
which a given row was selected. It's probably overcoding if a simple OR
will meet the requirements.

On Sun, Mar 14, 2021 at 8:46 AM Niels Liisberg <nli@xxxxxxxxxxxxxxxxx>
wrote:

Always use union all except when you really need to filter out double.. in
explain you will notice an extra sort step that removes the double
occurrence if any.

fre. 12. mar. 2021 kl. 22.48 skrev Peter Dow <petercdow@xxxxxxxxx>:

And some people tend to not understand the difference between a UNION

and a

JOIN.

x years ago (I don't remember how many), I didn't even know there was a
UNION, and then I had to figure out the difference between UNION and
UNION ALL :)

JOIN is also interesting -- I'm not sure when I learned you could use a
constant, e.g. flda = 'Y' in the JOIN ON clause. Makes JOIN ON sort of
like a WHERE clause just for the JOIN process.

--
*Peter Dow* /
Dow Software Services, Inc.
909 793-9050
petercdow@xxxxxxxxx <mailto:petercdow@xxxxxxxxx>
pdow@xxxxxxxxxxxxxx <mailto:pdow@xxxxxxxxxxxxxx> /
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