Talk:Intersection (set theory)
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Why are so many SQL implementations incomplete in so many aspects? Is there a reason for why INTERSECT ALL is not implemented in other versiond of SQL, such as performance, complexity or lack of demand that can be inserted into this article? Zaphraud 05:26, 30 May 2007 (UTC)
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I have the same problem comprehending intersection. To me it doesnt seem like a viable operation because once you put a "line"/marker in the middle of a box etc, the 2 small rectangles hence formed are seperate set.
so for example if I had a set of "all people in the school" and I wanted to make a set of all girls in the school I could use references to the people in the database, but then the "reference" itself is pointing to some memory cell etc, so I am actually making another set which contains refrences to a set of memory cells which have girls. Is that correct?
Likewise, if I have a set of all people who wear red ties to school, then I have another set whose elements are memory locations of the people who wear red ties to school.
Now if I want to find all the girls who wear red ties to school, then either I do search on the set of girls or the set of girls or the set of reds to find the matching.
The answer I get is a set of memory locations of the girls wearing red ties which I have to "store" in another memory location.
This set may contain elements of the set girl and the elements of the girl red, but however, this is a set seperate from the base set of girls and red ties. I mean one could also say that set contains ref to memory cells from the original set, but each of these references is always stored in a seperate set of cells..so it is indeed a seperate set.
Hence intersection cannot be a single step operation ever. It is like saying A.B is a subset of B, whereas in any digital circuit, one can tell you that A.B and B will have 2 seperate outcomes (they need 2 seperate LEDs to be percieved)
You can say B and B.A are the 2 events, however one would still say B is different from B.A , just like the domain name a.com is different from b.a.com
Note even if b belongs to a.com, it is a seperate entity and cannot be called a.com, it is called b.a.com —Preceding unsigned comment added by Alokdube (talk • contribs) 06:37, 30 June 2008 (UTC)
Please note the same logic applies when you consider a set of points on f(x,y)=0 and g(x,y)=0 The locus of points on their intersection is GF(x,y)=f(x,y)^2 + g(x,y)^2 =0 is different from each individual locus. That is precisely where the difference starts. If you have a window with a frame in it, the frame is different from the window, you will call it as window.frame only. It may inherit some properties from the parent window, but it is a seperate entity. The button click on the frame is an event on the frame. —Preceding unsigned comment added by Alokdube (talk • contribs) 06:53, 30 June 2008 (UTC)
