Re:Say no to Venn diagrams when explaining SQL joins (2016)
by ryanmonroe on Saturday January 12, 2019 @12:18PM
(#18892136)
f you have one set with 5 elements and another with 10, the set difference cannot have 13 elements.
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In anticipation of some possible technical replies, let me be more explicit:
It isn't a set difference, no matter how you view it.
Viewpoint 1:
The original lists of objects are not actually sets because the elements are not distinct. From this viewpoint, it isn't a set difference because they aren't even sets to begin with.
Viewpoint 2:
There is an implicit "row number" feature of each object so in that sense the objects are distinct and do form sets. From this viewpoint, it still isn't a set difference. If you have one set with 5 elements and another with 10, the set difference cannot have 13 elements.
-------
In anticipation of some possible technical replies, let me be more explicit:
It isn't a set difference, no matter how you view it.
Viewpoint 1: The original lists of objects are not actually sets because the elements are not distinct. From this viewpoint, it isn't a set difference because they aren't even sets to begin with.
Viewpoint 2: There is an implicit "row number" feature of each object so in that sense the objects are distinct and do form sets. From this viewpoint, it still isn't a set difference. If you have one set with 5 elements and another with 10, the set difference cannot have 13 elements.