Relational Databases
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Transcript of Relational Databases
![Page 1: Relational Databases](https://reader036.fdocuments.us/reader036/viewer/2022082818/56812c5f550346895d90ed4c/html5/thumbnails/1.jpg)
Jennifer Widom
Relational Databases
Querying Relational Databases
![Page 2: Relational Databases](https://reader036.fdocuments.us/reader036/viewer/2022082818/56812c5f550346895d90ed4c/html5/thumbnails/2.jpg)
Jennifer Widom
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
![Page 3: Relational Databases](https://reader036.fdocuments.us/reader036/viewer/2022082818/56812c5f550346895d90ed4c/html5/thumbnails/3.jpg)
Jennifer Widom
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
![Page 4: Relational Databases](https://reader036.fdocuments.us/reader036/viewer/2022082818/56812c5f550346895d90ed4c/html5/thumbnails/4.jpg)
Jennifer Widom
Querying Relational Databases
Queries return relations (“compositional”, “closed”)
![Page 5: Relational Databases](https://reader036.fdocuments.us/reader036/viewer/2022082818/56812c5f550346895d90ed4c/html5/thumbnails/5.jpg)
Jennifer Widom
Querying Relational DatabasesQuery Languages Relational Algebra
SQL
IDs of students with GPA > 3.7 applying to Stanford
Select Student.IDFrom Student, ApplyWhere Student.ID=Apply.IDAnd GPA>3.7 and college=‘Stanford’