Stairway to T-SQL DML Level 5: The Mathematics of SQL: Part 2

  • Fiacre Lenehan

    Mr or Mrs. 500

    Points: 584

    A very clear and informative article. A minor point is that the Figure numbers appear to be incorrect in the INNER Join Operator and OUTER JOIN Operator sections

  • Greg Larsen

    SSC-Insane

    Points: 20610

    I reviewed the article text and your comment and I'm not following what part of the article has incorrect figure numbers. Would you please explain a little further so I can get the article corrected so it contains references to figures that a accurate.

    Thank you

    Greg

    Gregory A. Larsen, MVP

  • Fiacre Lenehan

    Mr or Mrs. 500

    Points: 584

    "as shown in the Venn diagram in Figure 5" should this be Figure 3?

    "INNER JOIN operation to return part 2 of Figure 6" should this be Figure 4?

  • Greg Larsen

    SSC-Insane

    Points: 20610

    Comments posted to this topic are about the item Stairway to T-SQL DML Level 5: The Mathematics of SQL: Part 2

    Gregory A. Larsen, MVP

  • Craig Thomson-419971

    SSC-Addicted

    Points: 429

    Thanks Gregory

    It's always useful to review the basics.

    I think a mathematical set regards any identical member as being the same thing, so in the diagrams there would only be one representative of any number.

    I don't know where that leaves us with UNION ALL though, it seems to break the rules.

    I'm happy to be corrected, I just scraped through my maths degree.

    Craig

  • john.mcginley

    SSC Rookie

    Points: 40

    Very clear explanation of things we use daily and may never think about. Former Republican governor of Wisconsin Scott Walker should have read this a year ago.

  • steve.homer@gmail.com

    Grasshopper

    Points: 23

    Thanks Gregory

    It's always useful to review the basics.

    I think a mathematical set regards any identical member as being the same thing, so in the diagrams there would only be one representative of any number.

    I don't know where that leaves us with UNION ALL though, it seems to break the rules.

    I'm happy to be corrected, I just scraped through my maths degree.

    Craig

    You're correct. Sets are defined as collections of unique elements. SQL however isn't set based, but rather based on bags (think Sets that allow duplicates).

    See any of Chris Date's books for long rants about this 🙂

  • mayoadams

    Newbie

    Points: 4

    I think this is a very good way to teach essentials, using mathematical objects leached of the connotations of the "real world".  Thank you.

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