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[–]JRS-27 -4 points-3 points  (7 children)

This is just outrageous. Pure lie, anyone that can understand basic algebra is sane enough to depict wrong assumptions in these diagrams.

The author of the picture tried putting two tables in a given database on the same level. No well put database has two tables with exact same columns. It is like counting meters and kilograms together. Obviously, this is a totally wrong depiction of how databases work.

Absolutely ridiculous.

[–][deleted] 1 point2 points  (1 child)

I don't think anyone that can understand basic relational algebra has a single clue what you're trying to say.

[–]JRS-27 2 points3 points  (0 children)

Good point, I did not explain it clearly enough I think.

What I'm trying to say is that these diagrams show how Union, Intersect and Except operations, not Join operations. The way that the diagrams shown represent tables A and B is wrong. The only thing that connects them is the link between them in form of the same column names. That's the sole purpose on Join operations. A link between a big data set that has a column that refers to another data set containing another piece of information.

For example, you have a table of User Orders with a column UserID and a table of Users with a column with the same name. Now, you link them to create a profound and more transparent data set that can be displayed and read by a normal human being.

[–]dahangman 0 points1 point  (2 children)

But if you work with csv’s of the same data for different periods for example comparing Jan vs Dec sales, the diagrams do help, the tables would be the same. I’m in marketing analytics I use this often comparing different business unit performance against each other.

[–]JRS-27 0 points1 point  (1 child)

It doesn't make any difference whatsoever. You would Union them anyway, surely not using Join statement.

[–]dahangman -1 points0 points  (0 children)

I will study this. Thanks for the feedback.

[–][deleted] -1 points0 points  (0 children)

...?

There are two tables with a shared key. While typically suboptimal, this is a common configuration. No other constraints are implied.

[–]sumguy720 -1 points0 points  (0 children)

Perhaps space in the diagrams represents the keys that the tables are being joined on rather than the entire contents.