Relational Databases Relational Algebra (2)

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Presentation transcript:

Relational Databases Relational Algebra (2) Set operators, renaming, notation

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

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

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

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

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

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

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

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

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

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

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

Relational Algebra (2) Relational Algebra summary