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The hardest part of joins is remembering which is which. Venn diagrams are used specifically because they solve that problem with the inner/outer/left/right terminology.

His visualizations ultimately help nothing. You have to stare at them for a while to see what the pattern is, but there's absolutely no mnemonic hook to remember what's what, so in the end all you learn from his visualizations are that there exist different ways to slice and dice the products of sets, which is already a given if you're trying to figure out what the differences are.




The author's diagrams aren't perfect either, but I think they are much more clear to novice coders about the real workings of joins.

Check this out, similar to the author's approach, but animated. This is the best visual of SQL joins I've ever found. https://news.ycombinator.com/item?id=16983007


For me, I still have no idea what the visual of a venn diagram is trying to tell me within the context of SQL. Just having a visual that I can't even understand does nothing to benefit the situation either.




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