Relational Algebra

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Презентация Relational Algebra

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Lecture 6. Relational algebra National Aviation University Computer Science Faculty Department of So
Lecture 6. Relational algebra National Aviation University Computer Science Faculty Department of Software Engineering
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CONTENTS Query languages in DB Properties of binary operations Relational algebra operations Example
CONTENTS Query languages in DB Properties of binary operations Relational algebra operations Examples Equivalent transformation and optimization of relational algebra expressions
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Query languages Language categories: procedural (HOW to receive) nonprocedural (WHAT to receive) For
Query languages Language categories: procedural (HOW to receive) nonprocedural (WHAT to receive) Formal languages: relational algebra relational calculus (tuple-oriented and domain-oriented)
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Relational algebra closure and properties of binary operations Property of binary relations: Operati
Relational algebra closure and properties of binary operations Property of binary relations: Operation  is commutative if А  В = B  A Operation  is associative if (А  В)  С = А  (В  С) …
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Relational algebra operations Basic operations: set-theoretic (union, intersection, difference) proj
Relational algebra operations Basic operations: set-theoretic (union, intersection, difference) projection selection cartesian product, join division Additional operations assignment renaming …
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Set-theoretic operations
Set-theoretic operations
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Union operation
Union operation
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Difference operation
Difference operation
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Intersection operation
Intersection operation
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Projection operation
Projection operation
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-comparability of attributes and tuples
-comparability of attributes and tuples
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Selection (restriction) operation
Selection (restriction) operation
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Cartesian product
Cartesian product
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Join operation
Join operation
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Join and natural join
Join and natural join
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Semijoin
Semijoin
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Image of the tuple
Image of the tuple
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Division operation (1)
Division operation (1)
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Division operation(2)
Division operation(2)
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Example of DB for RA queries FAC (FNo, Name, Dean, Bld, Fund) DEP (DNo, FNo, Name, Head, Bld, Fund)
Example of DB for RA queries FAC (FNo, Name, Dean, Bld, Fund) DEP (DNo, FNo, Name, Head, Bld, Fund) TCH (TNo, DNo, Name, Post, Tel, Salary, Comm) GRP (GNo, DNo, Course, Num, Quantity, CurNo) SBJ …
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Examples of queries in RA (1)
Examples of queries in RA (1)
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Examples of queries in RA (2)
Examples of queries in RA (2)
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Examples of queries in RA (3)
Examples of queries in RA (3)
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Examples of division operation
Examples of division operation
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Additional operations Additional operations Assignment Renaming Generalized projection Outer join …
Additional operations Additional operations Assignment Renaming Generalized projection Outer join …
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Assignment operation
Assignment operation
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Rename operation
Rename operation
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Generalized projection operation
Generalized projection operation
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Outer join
Outer join
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Outer join – example of ordinary join
Outer join – example of ordinary join
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Left outer join
Left outer join
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Relational Algebra, слайд 32
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Full outer join
Full outer join
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Equivalent transformations of relational expressions 1) Commutativity of selection: σF(σG(R))=σG(σF(
Equivalent transformations of relational expressions 1) Commutativity of selection: σF(σG(R))=σG(σF(R))=σF&G(R) 2) Commutativity of selection and projection: G(σF(R))=σF(G(R))=σF&G(R), если …
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Optimization of RA expressions
Optimization of RA expressions
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General rules of RA expressions optimization General rules of RA expressions optimization: Transform
General rules of RA expressions optimization General rules of RA expressions optimization: Transform each selection σF1&. . . &Fn(E) to the sequence of selections σF1(. . . σFn(E)) Move each …
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Relational Algebra: Summary Relational Algebra: Formal language for handling data in relational mode
Relational Algebra: Summary Relational Algebra: Formal language for handling data in relational model Procedural language, how to retrieve data No practical relevance for querying DB Formal basis for …


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