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Relational Databases Relational Algebra (2)
Set operators, renaming, notation
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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) College Student Apply cName state enr sID sName GPA HS sID cName major dec
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Relational Algebra (2) Union operator
List of college and student names College Student Apply cName state enr sID sName GPA HS sID cName major dec
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Relational Algebra (2) Difference operator
IDs of students who didn’t apply anywhere IDs and names of students who didn’t apply anywhere College Student Apply cName state enr sID sName GPA HS sID cName major dec
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Intersection operator
Relational Algebra (2) Intersection operator Names that are both a college name and a student name College Student Apply cName state enr sID sName GPA HS sID cName major dec
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Intersection doesn’t add expressive power (1)
Relational Algebra (2) Intersection doesn’t add expressive power (1) College Student Apply cName state enr sID sName GPA HS sID cName major dec
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Intersection doesn’t add expressive power (2)
Relational Algebra (2) Intersection doesn’t add expressive power (2) College Student Apply cName state enr sID sName GPA HS sID cName major dec
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Relational Algebra (2) Rename operator 1. 2. 3. College Student Apply
cName state enr sID sName GPA HS sID cName major dec
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To unify schemas for set operators
Relational Algebra (2) Rename operator To unify schemas for set operators List of college and student names College Student Apply cName state enr sID sName GPA HS sID cName major dec
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For disambiguation in “self-joins”
Relational Algebra (2) Rename operator For disambiguation in “self-joins” Pairs of colleges in same state College Student Apply cName state enr sID sName GPA HS sID cName major dec
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Assignment statements – Pairs of colleges in same state
Relational Algebra (2) Alternate notation (1) Assignment statements – Pairs of colleges in same state College Student Apply cName state enr sID sName GPA HS sID cName major dec
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Expression tree – GPAs of students applying to CS in CA
Relational Algebra (2) Alternate notation (2) Expression tree – GPAs of students applying to CS in CA College Student Apply cName state enr sID sName GPA HS sID cName major dec
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Relational Algebra (2) Relational Algebra summary
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