This document discusses relational algebra operations including set operators like union, difference, and intersection. It describes how relational algebra queries apply these operators to relations and produce a resulting relation. Specifically, it covers how the rename operator can be used to unify relation schemas for set operations or disambiguate relations in self-joins. The document also presents alternate notations for relational algebra including assignment statements and expression trees.

1. Jennifer Widom
Relational Databases
Relational Algebra (2)
Set operators, renaming,
notation

2. Jennifer Widom
Relational Algebra (2)
Relational algebra query (expression) on set of
relations produces relation as a result
College(cName,state,enrollment)
Student(sID,sName,GPA,sizeHS)
Apply(sID,cName,major,decision)
cName state enr sID sName GPA HS sID cName major dec
College Student Apply

3. Jennifer Widom
Union operator
List of college and student names
cName state enr sID sName GPA HS sID cName major dec
College Student Apply
Relational Algebra (2)

4. Jennifer Widom
Difference operator
IDs of students who didn’t apply anywhere
cName state enr sID sName GPA HS sID cName major dec
College Student Apply
Relational Algebra (2)
IDs and names of students who didn’t apply anywhere

5. Jennifer Widom
Intersection operator
Names that are both a college name and a student name
cName state enr sID sName GPA HS sID cName major dec
College Student Apply
Relational Algebra (2)

6. Jennifer Widom
Intersection doesn’t add expressive power (1)
cName state enr sID sName GPA HS sID cName major dec
College Student Apply
Relational Algebra (2)

7. Jennifer Widom
Intersection doesn’t add expressive power (2)
cName state enr sID sName GPA HS sID cName major dec
College Student Apply
Relational Algebra (2)

8. Jennifer Widom
Rename operator
1.
2.
3.
cName state enr sID sName GPA HS sID cName major dec
College Student Apply
Relational Algebra (2)

9. Jennifer Widom
Rename operator
To unify schemas for set operators
cName state enr sID sName GPA HS sID cName major dec
College Student Apply
Relational Algebra (2)
List of college and student names

10. Jennifer Widom
Rename operator
For disambiguation in “self-joins”
cName state enr sID sName GPA HS sID cName major dec
College Student Apply
Relational Algebra (2)
Pairs of colleges in same state

11. Jennifer Widom
Alternate notation (1)
Assignment statements – Pairs of colleges in same state
cName state enr sID sName GPA HS sID cName major dec
College Student Apply
Relational Algebra (2)

12. Jennifer Widom
Alternate notation (2)
Expression tree – GPAs of students applying to CS in CA
cName state enr sID sName GPA HS sID cName major dec
College Student Apply
Relational Algebra (2)

13. Jennifer Widom
Relational Algebra summary
Relational Algebra (2)
Webcam Video
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