442_Review

442_Review - Review: SQL Relational Algebra 198:442...

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Review: SQL – Relational Algebra 198:442
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Declarative vs. Operative QL Declarative Relational Calculus SQL Operative Relational Algebra Describes the output of the query Describes operations applied to data
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Relational Algebra Basic operations: Selection ( ) Selects a subset of rows from relation. Projection ( ) Deletes unwanted columns from relation. Cross-product ( ) Allows us to combine two relations. Set-difference ( ) Tuples in reln. 1, but not in reln. 2. Union ( ) Tuples in reln. 1 and in reln. 2. Additional operations: Intersection, join , division, renaming: Not essential, but (very!) useful. Since each operation returns a relation, operations can be composed ! (Algebra is “closed”.) σ π - ×
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Basic SQL Query relation-list A list of relation names (possibly with a range- variable after each name). target-list A list of attributes of relations in relation-list qualification Comparisons (Attr op const or Attr1 op Attr2,
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This note was uploaded on 02/24/2011 for the course CS 442 taught by Professor Mlittman during the Fall '08 term at Rutgers.

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442_Review - Review: SQL Relational Algebra 198:442...

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