Set Operations
Abstract
Since SQL is based on sets, it includes classic set operations, with extensions for multisets.
Keywords
ALL
DISTINCT
EXCEPT
EXCEPT ALL
INTERSECT
INTERSECT ALL
Multisets (bags)
Proper subsets
Redundant duplicates
Set equality
UNION
UNION ALL
Union compatible
By set operations, I mean union, intersection, and set differences where the sets in SQL are tables. These are the basic operators used in elementary set theory, which has been taught in the United States public school systems for decades. Since the relational model is based on sets, you would expect that SQL would have had a good variety of set operators. But there is a problem in SQL that you did not have in high school set theory. SQL tables are multisets ...
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