CSE 278 Lecture Notes - Lecture 11: Semicolon, Multiset, Type System
15 Oct 2018
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Document Summary
Attributed displayed in any order as in table. Table is representation of schema of relation and its tuples. Relation- think of as table that has been instantiated with tuples. May be represented by instantiated tables, by permuting rows and columns. Sometimes it"s convenient to see relations not as a set but as a bag (multiset) of tuples, in which tuple may be repeated any number of times. Relations are dynamic- tuples of a relation will be constantly added and deleted using the dml. However the schemas of non-temporary relations tend to stay. Concrete relation, very similar to our abstract models in sql is called a table. There are also views, which are virtual or constructed from tables. Temporary tables, constructed by sql as part of the job of executing queries. Keys: attributes whose values, if non null, are not repeated and determine the value of the rest of the attributes. A key is a very simple form of an index.
