lecture 7.pptx - DATABASE MANAGEMENT SYSTEMS 1 Lecture 7 BRIEF RECAP Relational Model Relational keys Primary key Foreign key Referential Actions on

lecture 7.pptx - DATABASE MANAGEMENT SYSTEMS 1 Lecture 7...

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BRIEF RECAP Relational Model Relational keys Primary key Foreign key Referential Actions on Foreign Keys Restrict Cascade Nullify Default 2
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INTRODUCTION Relational algebra and relational calculus are formal languages associated with the relational model. Informally, relational algebra is a (high-level) procedural language and relational calculus a non-procedural language. However, formally both are equivalent to one another. 4
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RELATIONAL ALGEBRA Relational algebra operations work on one or more relations to define another relation without changing the original relations. Both operands and results are relations, so output from one operation can become input to another operation. Allows expressions to be nested, just as in arithmetic. This property is called closure . 5
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RELATIONAL ALGEBRA Five basic operations in relational algebra: Selection, Projection, Cartesian product, Union, and Set Difference. These perform most of the data retrieval operations needed. Also have Join, Intersection, and Division operations, which can be expressed in terms of 5 basic operations. 6
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- RELATIONAL ALGEBRA OPERATIONS Select Project Rename Union Difference Intersection Assignment Cartesian Product Join Outer Union Composition of Operators Aggregate Functions Null Values 8
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SELECTION (OR RESTRICTION) predicate (R) Works on a single relation R and defines a relation that contains only those tuples (rows) of R that satisfy the specified condition ( predicate ).
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