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Kumarapathirana K. P. S. D. Section 3.0

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Introduction The basic set of operations for the relational model is the relational algebra User specifies basic retrieval requests The result of a retrieval is a new relation The algebra operations thus produce new relations

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Introduction A sequence of relational algebra operations forms a relational algebra expression Why …….. ? –I–It provides a formal foundation for relational model operations –I–It is used as a basis for implementing and optimizing queries –S–Some of its concepts are incorporated into the SQL

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Two types –O–Operations developed specifically for relational databases Eg:SELECT, PROJECT and JOIN –S–Set operations from mathematical set theory Eg: UNION, INTERSECTION, SET DIFFERENCE, and CARTESIAN PRODUCT

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Two types –U–Unary operations Operate on single relation Eg:SELECT and PROJECT –B–Binary operations Operate on two relations Eg: JOIN, UNION, INTERSECTION, MINUS ….

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Unary Relational Operations SELECT –T–This operation is used to select a subset of the tuples from a relation that satisfy a selection condition –A–A filter –T–The SELECT operation is a horizontal partition of the relation into two sets of tuples Those tuples that satisfy the condition and are selected Those tuples that do not satisfy the condition and are discarded.

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–R–Representation σ

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The relation resulting from the SELECT operation has the same attributes as R

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Example : σ FNAME = Nimal (R) SELECT * FROM EMPLOYEE WHERE FNAME = ‘Nimal’ EIDFNAMEMNAMELNAMEAGEDEPARTMENT 12NimalKumaraLiyanage46Finance 34SunimalKeerthiPerera33Production 22LalithVithanaNimalasena45Finance 35ChathuraShanakaSilva20Sales 11WicramaSapumalAmarathunga23Marketing

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EIDFNAMEMNAMELNAMEAGEDEPARTMENT 12NimalKumaraLiyanage46Finance 34SunimalKeerthiPerera33Production 22LalithVithanaNimalasena45Finance 35ChathuraShanakaSilva20Sales 11WicramaSapumalAmarathunga23Marketing EIDFNAMEMNAMELNAMEAGEDEPARTMENT 12NimalKumaraLiyanage46Finance 22LalithVithanaNimalasena45Finance To select the EMPLOYEE tuples whose department is ‘Finance’,

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EIDFNAMEMNAMELNAMEAGEDEPARTMENT 12NimalKumaraLiyanage46Finance 34SunimalKeerthiPerera33Production 22LalithVithanaNimalasena45Finance 35ChathuraShanakaSilva20Sales 11WicramaSapumalAmarathunga23Marketing EIDFNAMEMNAMELNAMEAGEDEPARTMENT 12NimalKumaraLiyanage46Finance 34SunimalKeerthiPerera33Production 22LalithVithanaNimalasena45Finance To select the EMPLOYEE tuples whose age is greater than 30

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The way the result is determined ……. –<–

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The number of tuples in the resulting relation is always less than or equal to the number of tuples in R |σ c (R)| <= |R| The SELECT operation is commutative σ

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A cascade of SELECT operations can be combined into a single SELECT operation with a conjunctive (AND) condition σ (σ (….(σ (R)) = σ AND AND …. AND (R)

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Exercise…. Find the students of IIT & CST degree program Find the 4 th year students whose degree program is SCT SIDFNAMEMNAMELNAMEDEGPROYEAR 12SahanNilankaPereraCST2 23NuwanLasanthaSilvaIIT3 45ChamaliNadeeKumariSCT4 50VipuliSamadhiPereraCST2 03NimaliPubuduPereraSCT4 11VishvaLakmalFernandoCST3 34LasithPiumalSilvaIIT2

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PROJECT –S–Selects certain columns from the table and discards the other columns –v–vertical partition of the relation into two relations: One has the needed columns (attributes) and contains the result of the operation The other contains the discarded columns

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–R–Representation ∏

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To list each employee's employee id, first and last name EIDFNAMEMNAMELNAMEAGEDEPARTMENT 12NimalKumaraLiyanage46Finance 34SunimalKeerthiPerera33Production 22LalithVithanaNimalasena45Finance 35ChathuraShanakaSilva20Sales 11WicramaSapumalAmarathunga23Marketing EIDFNAMEMNAME 12NimalKumara 34SunimalKeerthi 22LalithVithana 35ChathuraShanaka 11WicramaSapumal

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If the attribute list includes only non-key attributes of R –D–Duplicate tuples are likely to occur –P–PROJECT operation removes any duplicate tuples Duplicate elimination –E–Eg: ∏ LNAME,AGE,DEPARTMENT (Employee) EIDFNAMEMNAMELNAMEAGEDEPARTMENT 12NimalKumaraLiyanage45Finance 34SunimalKeerthiPerera33Production 22LalithVithanaLiyanage45Finance 35ChathuraShanakaSilva20Sales 11WicramaSapumalAmarathunga23Marketing LNAMEAGEDEPARTMENT Liyanage45Finance Perera33Production Liyanage45Finance Silva20Sales Amarathunga23Marketing LNAMEAGEDEPARTMENT Liyanage45Finance Perera33Production Silva20Sales Amarathunga23Marketing

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The number of tuples in a relation resulting from a PROJECT operation is always less than or equal to the number of tuples in R If the projection list is a superkey of R, the resulting relation has the same number of tuples as R ∏ list1 (∏ list2 R) = ∏ list1 (R) If list 2 contains list 1

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Exercise…. Find the names of students of all the students Find id and the degree program of all the students SIDFNAMEMNAMELNAMEDEGPROYEAR 12SahanNilankaPereraCST2 23NuwanLasanthaSilvaIIT3 45ChamaliNadeeKumariSCT4 50VipuliSamadhiPereraCST2 03NimaliPubuduPereraSCT4 11VishvaLakmalFernandoCST3 34LasithPiumalSilvaIIT2

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Sequences of Operations Several relational algebra operations can be applied one after the other –W–We can write the operations as a single relational algebra expression –W–We can apply one operation at a time and create intermediate result relations We must give names to the relations that hold the intermediate results.

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Eg: –R–Retrieve the first name, last name, and age of all employees who work in finance department ∏ FNAME,LNAME,AGE ( σ DEPARTMENT = FINANCE (Employee)) EIDFNAMEMNAMELNAMEAGEDEPARTMENT 12NimalKumaraLiyanage45Finance 34SunimalKeerthiPerera33Production 22LalithVithanaLiyanage45Finance 35ChathuraShanakaSilva20Sales 11WicramaSapumalAmarathunga23Marketing FNAMELNAMEAGE NimalLiyanage45 LalithLiyanage45

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Eg: –R–Retrieve the first name, last name, and age of all employees who work in finance department FinDept_Emp σ

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Exercise…. Find the names of 2 nd year students of IIT & CST degree program Find the first name and the degree program of students with sid 12, 50 and 34 SIDFNAMEMNAMELNAMEDEGPROYEAR 12SahanNilankaPereraCST2 23NuwanLasanthaSilvaIIT3 45ChamaliNadeeKumariSCT4 50VipuliSamadhiPereraCST2 03NimaliPubuduPereraSCT4 11VishvaLakmalFernandoCST3 34LasithPiumalSilvaIIT2

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It is often simpler to break down a complex sequence of operations We can also use this technique to rename the attributes in the intermediate and result relations FinDept_Emp σ

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RENAME –R–Rename either the relation name or the attribute names, or both –R–Repesentation ρ S(B1, B2,.... Bn) (R) ρ S (R) ρ (B1,B2,...,Bn) (R)

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Eg: FinDept_Emp σ

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Exercise…. Find the names of 2 nd year students of IIT & CST degree program name them as FIRSTNAME, MIDDLENAME and LASTNAME Find the ids and the degree program of students with sid 12, 50 and 34 name the new relation as ENROLLMENTS with the column names ID and ENROLLED_DEGREE_PROGRAM SIDFNAMEMNAMELNAMEDEGPROYEAR 12SahanNilankaPereraCST2 23NuwanLasanthaSilvaIIT3 45ChamaliNadeeKumariSCT4 50VipuliSamadhiPereraCST2 03NimaliPubuduPereraSCT4 11VishvaLakmalFernandoCST3 34LasithPiumalSilvaIIT2

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Relational Algebra Operations From Set Theory UNION Result1 = ∏

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RESULT = RESULT1 υ RESULT2 EID EID RESULT1RESULT2 EID RESULT Duplicate tuples are eliminated

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–T–The UNION operation produces the tuples that are in either RESULT1 or RESULT2 or both –T–Two relations R(A1, A2,..., An) and S(B1,B2,…, Bn) are said to be union compatible If they have the same degree n If dom(Ai) = dom(Bi) for 1< i < n –c–commutative operations R υ S = S υ R

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Exercise…. Find the employees who works on project ‘345’ Find the employees who works on project ‘678’ Find the employees who works on project ‘345’ or ‘678’ with the results of the above two answers. EIDFNAMEMNAMELNAME 12SahanNilankaPerera 23NuwanLasanthaSilva 45ChamaliNadeeKumari EIDPROJECTID

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INTERSECTION Result1 = ∏

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RESULT= RESULT1 RESULT2 EID EID RESULT1RESULT2 EID RESULT υ

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Result is a relation that includes all tuples that are in both relations commutative operations R S = S R associative operations (R S) T = R (S T) υ υ υυυυ

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Exercise…. Find the employees who works on project ‘345’ Find the employees who works on project ‘678’ Find the employees who works on project ‘345’ & ‘678’ with the results of the above two answers. EIDFNAMEMNAMELNAME 12SahanNilankaPerera 23NuwanLasanthaSilva 45ChamaliNadeeKumari EIDPROJECTID

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MINUS / SET DIFFERENCE Result1 = ∏

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RESULTX = RESULT1 – RESULT2 RESULTY = RESULT2 – RESULT1 EID EID RESULT1RESULT2 EID RESULTY EID RESULTX

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The result of this operation, denoted by R - S, is a relation that includes all tuples that are in R but not in S not commutative R - S ≠ S - R

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Exercise…. Find the employees who works on project ‘345’ Find the employees who works on project ‘678’ Find the employees who is working on project ‘345’ and not working on project ‘678’ with the results of the above two answers. EIDFNAMEMNAMELNAME 12SahanNilankaPerera 23NuwanLasanthaSilva 45ChamaliNadeeKumari EIDPROJECTID

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The CARTESIAN PRODUCT Operation –K–Known as CROSS PRODUCT or CROSS JOIN –B–Binary set operation –T–The relations do not have to be union compatible –C–Combines tuples from two relations in a combinatorial fashion –d–denoted by X –T–The result of R(A 1, A 2,..., A n ) X S(B 1, B 2,..., B m ) will be Q(A 1, A 2,..., A n, B 1, B 2,..., B m ) –I–If R has n R tuples, and S has n S tuples, then R x S will have n R * n S tuples

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SIDNameAgeDegreeProgram 112Sahan21CST 212Achini21IIT 234Nalaka22SCT DegreeProgram Code DegreeProgram Name CSTComputer Science & Technology IITIndustrial Information Technology SCTScience & Technology STUDENT DEGREEPROGRAM Eg :

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SIDNameAgeDegreeProgramDegreeProgramCodeDegreeProgramName 112Sahan21CST Computer Science & Technology 212Achini21IIT CSTComputer Science & Technology 234Nalaka22SCT CSTComputer Science & Technology 112Sahan21CST IITIndustrial Information Technology 212Achini21IIT Industrial Information Technology 234Nalaka22SCT IITIndustrial Information Technology 112Sahan21CST SCTScience & Technology 212Achini21IIT SCTScience & Technology 234Nalaka22SCT Science & Technology STUDENT X DEGREEPROGRAMINTERMEDIATE_RESULT

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∏ SID,NAME,AGE,DEGREEPROGRAMNAME ( σ DegreeProgramCode = DegreeProgram (INTERMEDIATE_RESULT)) SIDNameAgeDegreeProgramName 112Sahan21 Computer Science & Technology 212Achini21 Industrial Information Technology 234Nalaka22 Science & Technology

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BINARY RELATIONAL OPERATIONS JOIN –D–Denoted by –C–Combine related tuples from two relations into single tuples. –A–Allows us to process relationships among relations –R–Representation S

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SIDNameAgeDegreeProgram 112Sahan21CST 212Achini21IIT 234Nalaka22SCT DegreeProgram Code DegreeProgram Name CSTComputer Science & Technology IITIndustrial Information Technology SCTScience & Technology STUDENT DEGREEPROGRAM Eg : INTERMEDIATERESULT SIDNameAgeDegreeProgramDegreeProgramCodeDegreeProgramName 112Sahan21CST Computer Science & Technology 212Achini21IIT Industrial Information Technology 234Nalaka22SCT Science & Technology INTERMEDIATERESULT STUDENT DEGREEPROGRAM RESULT ∏ SID,NAME,AGE,DEGREEPROGRAMNAME (INTERMEDIATERESULT) SIDNameAgeDegreeProgramName 112Sahan21 Computer Science & Technology 212Achini21 Industrial Information Technology 234Nalaka22 Science & Technology RESULT

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SIDNameAgeDegreeProgramName 112Sahan21 Computer Science & Technology 212Achini21 Industrial Information Technology 234Nalaka22 Science & Technology SIDNameAgeDegreeProgram 112Sahan21CST 212Achini21IIT 234Nalaka22SCT DegreeProgram Code DegreeProgram Name CSTComputer Science & Technology IITIndustrial Information Technology SCTScience & Technology STUDENT DEGREEPROGRAM Eg : RESULT ∏ SID,Name,Age,DegreeProgramName ( STUDENT DegreeProgram = DegreeProgramCode DEGREEPROGRAM) RESULT

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A general join condition is of the form AND AND... AND

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Equi Join –W–Where only equality comparisons is used

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Natural Join –T–The two join attributes have the same name in both relations –I–If not, a renaming operation is applied first –D–Denoted by * –R–Representation R * S R * ρ

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SIDNameAgeDegreeProgramName 112Sahan21 Computer Science & Technology 212Achini21 Industrial Information Technology 234Nalaka22 Science & Technology SIDNameAgeDegreeProgram 112Sahan21CST 212Achini21IIT 234Nalaka22SCT DegreeProgram Code DegreeProgram Name CSTComputer Science & Technology IITIndustrial Information Technology SCTScience & Technology STUDENT DEGREEPROGRAM Eg : RESULT STUDENT * ρ (DegreeProgram, Name) DEGREEPRGRAM RESULT

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SIDNameAgeDegreeProgramName 112Sahan21 Computer Science & Technology 212Achini21 Industrial Information Technology 234Nalaka22 Science & Technology SIDNameAgeDegreeProgram 112Sahan21CST 212Achini21IIT 234Nalaka22SCT DegreeProgram Code DegreeProgram Name CSTComputer Science & Technology IITIndustrial Information Technology SCTScience & Technology STUDENT DEGREEPROGRAM Eg : DEGREE_PRO ρ (DegreeProgram, Name) DEGREEPRGRAM RESULT STUDENT * DEGREE_PRO RESULT

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OUTER JOIN –W–When we want to keep all the tuples in R, or all those in S, or all those in both relations in the result of the JOIN –3–3 types LEFT OUTER JOIN RIGHT OUTER JOIN FULL OUTER JOIN

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–A–An extension of the join operation that avoids loss of information. –U–Uses null values: Null signifies that the value is unknown or does not exist

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Relation loan Relation borrower customer-nameloan-number Jones Smith Hayes L-170 L-230 L loan-numberamount L-170 L-230 L-260 branch-name Downtown Redwood Perryridge

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Inner Join loan Borrower loan-numberamount L-170 L customer-name Jones Smith branch-name Downtown Redwood Jones Smith null loan-numberamount L-170 L-230 L customer-namebranch-name Downtown Redwood Perryridge Left Outer Join loan Borrower

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Right Outer Join loan borrower Full Outer Join loan-numberamount L-170 L-230 L null customer-name Jones Smith Hayes branch-name Downtown Redwood null loan-numberamount L-170 L-230 L-260 L null customer-name Jones Smith null Hayes branch-name Downtown Redwood Perryridge null

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Aggregation function – Takes a collection of values and returns a single value as a result. avg: average value min: minimum value max: maximum value sum: sum of values count: number of values Aggregate operation in relational algebra – Representation G1, G2, …, Gn g F1( A1 ), F2( A2 ),…, Fn( An ) (E)

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LOANNOBRANCHAMOUNT Colombo23, Badulla34, Kandy12, Colombo23, Kandy12,332 g sum(AMOUNT) (ACCOUNT) AMOUNT 105,299 BRANCH g sum(AMOUNT) (ACCOUNT) BRANCHAMOUNT Colombo Badulla34,211 Kandy24545

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Aggregate Functions (Cont.) Result of aggregation does not have a name – Can use rename operation to give it a name – For convenience, we permit renaming as part of aggregate operation branch-name g sum(balance) as sum-balance (account)

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