7 ms·

I always thought venn diagram was a good representation but I think I was wrong. Edit: Why did I get down voted? :)

ericHosick 3y ago
I would also like to know why you are getting downvoted. Even wikipedia uses a Venn diagram to explain JOIN https://en.wikipedia.org/wiki/Join_(SQL) https://en.wikipedia.org/wiki/Join_(SQL) . Not trying to use an argument from authority but just pointing out that this is not unheard of.
- radiospiel 3y ago
  Venn diagrams are a terrible way to describe join types (and, tbh, I don’t understand why Wikipedia has these) because it makes it look like applying an 1:1 relationship. In a M:N relationship „artefacts“ (for lack of better words) of both tables would appear multiple times, and the venn diagram obscures this fact
  - ericHosick 3y ago
    > because it makes it look like applying an 1:1 relationship. People can form different mental models of the same abstraction so I see what you are saying I've never seen it that way because "Venn diagrams do not generally contain information on the relative or absolute sizes (cardinality) of sets." (see https://en.wikipedia.org/wiki/Venn_diagram https://en.wikipedia.org/wiki/Venn_diagram).
somat 3y ago
Because a venn diagram does not describe join mechanics well. A venn diagram does however describes the UNION, INTERSECT, EXCEPT part of sql. https://blog.jooq.org/say-no-to-venn-diagrams-when-explaining-joins/ https://blog.jooq.org/say-no-to-venn-diagrams-when-explainin... And more meta, it is an innocent slightly incorrect statement, stuff like that should not be down voted, reply with a correction. Save down votes for outright malicious posts.
spiffytech 3y ago
I've always found Coding Horror's Venn diagram depiction of SQL joins quite enlightening: https://blog.codinghorror.com/a-visual-explanation-of-sql-joins/ https://blog.codinghorror.com/a-visual-explanation-of-sql-jo...

I would also like to know why you are getting downvoted. Even wikipedia uses a Venn diagram to explain JOIN https://en.wikipedia.org/wiki/Join_(SQL) https://en.wikipedia.org/wiki/Join_(SQL) . Not trying to use an argument from authority but just pointing out that this is not unheard of.

radiospiel 3y ago
Venn diagrams are a terrible way to describe join types (and, tbh, I don’t understand why Wikipedia has these) because it makes it look like applying an 1:1 relationship. In a M:N relationship „artefacts“ (for lack of better words) of both tables would appear multiple times, and the venn diagram obscures this fact
- ericHosick 3y ago
  > because it makes it look like applying an 1:1 relationship. People can form different mental models of the same abstraction so I see what you are saying I've never seen it that way because "Venn diagrams do not generally contain information on the relative or absolute sizes (cardinality) of sets." (see https://en.wikipedia.org/wiki/Venn_diagram https://en.wikipedia.org/wiki/Venn_diagram).

somat 3y ago

Because a venn diagram does not describe join mechanics well. A venn diagram does however describes the UNION, INTERSECT, EXCEPT part of sql. https://blog.jooq.org/say-no-to-venn-diagrams-when-explaining-joins/ https://blog.jooq.org/say-no-to-venn-diagrams-when-explainin... And more meta, it is an innocent slightly incorrect statement, stuff like that should not be down voted, reply with a correction. Save down votes for outright malicious posts.

spiffytech 3y ago

I've always found Coding Horror's Venn diagram depiction of SQL joins quite enlightening: https://blog.codinghorror.com/a-visual-explanation-of-sql-joins/ https://blog.codinghorror.com/a-visual-explanation-of-sql-jo...