SQL Join Types

[Uncle Gizmo]

As to displaying the SQL as a venn diagram, well, it's a no brainer for me, everyone is familiar with venn diagrams since school, so the venn diagrams display the information in a medium familiar to all.

 

[Gasman]

As to displaying the SQL as a venn diagram, well, it's a no brainer for me, everyone is familiar with venn diagrams since school, so the venn diagrams display the information in a medium familiar to all.

I found out when I went to college, that I was the only person in my class that had not done calculus previously.

Not sure I even saw a Venn diagram as well. , but then my memory is quite bad these days.

However is does appear to be a recognised method to others?

 

[Pat Hartman]

@isladogs I must have sent it to you years ago when I first created it since that is the menu page. I think I built the original in 2014 but the database was never publicly posted.

I never saw the sample by Steve Stedman, nor any other sample using Venn diagrams to depict join types. Can you tell how old it is? I'm curious. Maybe I've never seen one because I've probably never searched for info on joins. Steve's sample takes the visualization to three tables. I wonder what he meant by the two tables picture. Maybe that is a union. I forgot to do a Union separately because I used the union in the Full Outer join. But I did include a cross join. Looks like I need to add the union to the database Thanks for that picture. I think I'll make the union as two circles on top of each other rather than side by side.

I also never saw the image @jdraw created.

Venn diagrams may be so last year but the substitute is a mystery to me. No one ever had to explain a Venn diagram to me. I understood the graphic as soon as I saw one for the first time.

I'm not sure when I saw my first Venn diagram. I'm pretty sure it wasn't in a math class. I didn't take Calculous either. And it wasn't a description of how joins work. It was probably a three circle picture showing the intersection of three things like Republicans/Democrats/Libertarians showing their shared and separate believes.

 

[isladogs]

I think you sent it to me some time ago after I mentioned my web page on Query Join Types.
A Google search for Access query join Venn diagrams gives a huge number of hits. I just chose one at random

 

[cheekybuddha]

Venn diagrams have been used to explain SQL joins for a long time.

Doesn't negate Pat's use of them; in fact, that's why they are used, they are the clearest representation and additionally help the user to understand the set based nature of SQL interactions.

 

[Pat Hartman]

I've never searched for joins so I've never seen any of those samples. Some of them are very similar to what I came up with. I'm happy with that. I've never seen them in any SQL or Access book either.
Thanks again

 

[Uncle Gizmo]

Pat's examples make use of aliases:-

tblPeople as A

tblLocation as B

I've never felt the need to use Aliases, but seeing Pat's examples with Aliases, l can see they add level of clarity which is very useful.

I will consider using Aliases in the future, as clarity in code is important.

 

[cheekybuddha]

This article is against using Venn diagrams to illustrate SQL joins, but I rather take the view of one of the commenters that their clarity and simplicity in explaining the concepts of different types of joins trump their inaccuracy.

 

[Uncle Gizmo]

I found out when I went to college, that I was the only person in my class that had not done calculus previously.

I struggle with the mechanics of words.

I have no idea about nouns, verbs, adjectives, etc ..

I discovered years later that this was because my school was running a government experiment on my year where we were following a different curriculum.

We were not taught traditional grammar.

This experiment has had very little effect on me up until I started to learn Spanish.

When the textbooks discussed Spanish in terms of nouns verbs adjectives and the like I had no idea what they were on about!

I wonder if you were unwittingly exposed to a similar alternative curriculum?

 

[Pat Hartman]

I don't think the RUS is represented by the full color circles. I would use two single circles. One on top of the other because there is no overlap. The whole point of the Venn diagram is to highlight the overlap between sets. Now that I said that. I do remember seeing Venn diagrams during the discussion of sets in advanced Algebra.