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Relational Databases

Relational Databases. Querying Relational Databases. Querying Relational Databases. Steps in creating and using a (relational) database 1 . Design schema; create using DDL 2 . “Bulk load” initial data 3 . Repeat: execute queries and modifications.

chelsea-yates
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Relational Databases

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  1. Relational Databases Querying Relational Databases

  2. Querying Relational Databases Steps in creating and using a (relational) database 1. Design schema; create using DDL 2. “Bulk load” initial data 3. Repeat: execute queries and modifications

  3. Querying Relational Databases Ad-hoc queries in high-level language • All students with GPA > 3.7 applying to Stanford and MIT only • All engineering departments in CA with < 500 applicants • College with highest average accept rate over last 5 years • Some easy to pose; some a bit harder • Some easy for DBMS to execute efficiently; some harder • “Query language” also used to modify data

  4. Querying Relational Databases Queries return relations (“compositional”, “closed”)

  5. Querying Relational Databases Query Languages • Relational Algebra • SQL IDs of students with GPA > 3.7 applying to Stanford Select Student.ID From Student, Apply Where Student.ID=Apply.ID And GPA>3.7 and college=‘Stanford’

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