Data Modeling and Databases Advanced SQL

transcript

DataModelingandDatabasesAdvancedSQL

GustavoAlonso,CeZhangSystemsGroupDepartmentofComputerScienceETHZürich

D-INFK,ETHZurich,DataModelingandDatabases 2

1. Wewillwritedowntheanswertoquestionsontheslides.

2. Keepsendingusyourquestionstothemailinglistsuchthatwecancompilethemandshareitwiththewholeclass.

Keepgivingusfeedback!

SQLWeSawsofarq SELECT… FROM… WHEREq Aggregationq Subquery

YoucandomoreinSQL!

q CorrelatedSubqueryq NULLValuesq Viewq Recursion

Acknowledgementq ManyexamplestakenfromJenniferWidom’sdatabaseclass:https://www.youtube.com/watch?v=uU7JBM3cAWU

Student

Assistant

PersNr

Semester

attends

Works-forProfessor

Lecture

teaches

requires

PersNr

follow-upprerequisite

University Schema

5D-INFK,ETHZurich,DataModelingandDatabases

RelationalModelof UniversitySchemaProfessor

PersNr Name Level Room2125 Meyer FP 2262126 Kossmann FP 2322127 Roscoe AP 3102133 Perrig AP 522134 Sorkine AP 3092136 Welzl FP 362137 Norrie FP 7

StudentLegi Name Semester

24002 Gerber 1825403 Zollinger 1226120 Frey 1026830 Küng 827550 Fehr 628106 Lustenberger 329120 Schweizer 229555 Meier 2

LectureNr Title CP PersNr

5001 Databases 4 21375041 Networks 4 21255043 Operating Systems 3 21265049 Programming 2 21254052 Architecture 4 21255052 Theory 3 21265216 Graphics 2 21265259 Distributed Systems 2 21335022 Formal Methods 2 21344630 Probability 4 2137

requiresPrerequisite Follow-up

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attendsLegi Nr

26120 500127550 500127550 405228106 504128106 505228106 521628106 525929120 500129120 504129120 504929555 502225403 5022

AssistantPerslNr Name Area Boss3002 Heinis Databases 21253003 Müller Theory 21253004 Kemme Networks 21263005 Frey Graphics 21273006 Peter Operating Systems 21273007 Kraska Formal Methods 2126

testsLegi Nr PersNr Grade

28106 5001 2126 1

25403 5041 2125 227550 4630 2137 2

NullValues(NULL=UNKNOWN)

select count (*)from Studentwhere (Semester<13) or (Semester>=13);

select count (*)from Student;

Arethese two queries equivalent?

NULLinSQLq InSQL,NULLrepresentsastate,notavalue

SELECT*FROMstudentsWHEREsemester=NULL;

q Thestandardisinconsistent,makingitdifficulttoapplyclearsemantics(examples:uniontreats“NULL”asbeingequaltoeachother).

q Implementationsofthestandardarealsoinconsistentamongthemselves(operationsinvolvingnulloverdifferentdatatypes)

q Nullvaluescreateanopenworldassumption(againsttheclosedworldassumptionoftherelationalmodel)

Workingwith NullValues1. Arithmetics:Propagatenull:If anoperand is null,the

result is null.Ø null +1->null

Ø null *0->null

2. Comparisons:Allcomparisons that involve anull value,evaluate to unknown.Ø null =null ->unknown

Ø null<13 -> unknown

Ø null >null ->unknown

3. Logic:Booleanoperators are evaluated using the followingtables (next slide):

¤ Omnibox entries now match saved profile names first. ¤ You can drag & drop text based content into the session now. ¤ OpenSSH upgraded to 7.6p1 (some older features dropped). ¤ The default terminal encoding has changed to UTF

SELECT(NULL>NULL)ISNULL;

nottrue falseunknown unknownfalse true

and true unknown falsetrue true unknown falseunknown unknown unknown falsefalse false false false

or true unknown falsetrue true true trueunknown true unknown unknownfalse true unknown false

4. where: Only tuples which evaluate to true are part of the query result. (unknown and false are equivalent here):

select count (*)from Studentwhere Semester<13 or Semester>=13;

5. group by: If exists, then there is a group for null.select count (*)

from Studentgroup by Semester;

Predicates with null:select count (*)from Studentwhere Semesteris null;

Workingwith NullValues

SyntacticSugar

select *from Studentwhere Semester > = 1 and Semester < = 6;

select *from Studentwhere Semester between 1 and 6;

select *from Studentwhere Semester in (2,4,6);

select Legi, ( case when Grade >= 5.5 then ´sehr gut´when Grade >= 5.0 then ´gut´when Grade >= 4.5 then ´befriedigend´when Grade >= 4.0 then áusreichendélse ńicht bestandenénd)

from tests;

q Behaves like aswitch:evaluate from topto bottomq No „break“needed because at most one clauseexecuted.

13D-INFK,ETHZurich,DataModelingandDatabases

ExamplefromOracleSELECTcust_last_name,CASEcredit_limitWHEN100THEN'Low'WHEN5000THEN'High'ELSE'Medium'ENDFROMcustomers;

Comparisonswithlikeq "%”representsanysequenceofcharacters(0ton)q "_”representsexactlyonecharacterq N.B.:Forcomparisonswith= ,%and_arenormalchars.

select *from Studentwhere Name like ´Kossman%´;

select distinct Namefrom Lecture l, attends a, Student swhere s.Legi = a.Legi and a.Nr = l.Nr

and l.Title like ´%systems%´;

ExamplesfromOracleSELECTsalaryFROMemployeesWHERElast_name LIKE'R%';

SELECTsalaryFROMemployeesWHERElast_name ='R%';

Joins inSQLq cross join: Cartesian productq natural join:q join or inner join:Theta-Joinq left,right or full outer join:outer join variants

select *from R1,R2where R1.A=R2.B;

select *from R1join R2 on R1.A=R2.B;

DataManipulationLanguage

Insert tuplesinsert into attends

select Legi, Nrfrom Student, Lecturewhere Title= `Logik´;

insert into Student (Legi, Name)values (28121, `Kaufmann´);

Deletionoftuples,Update

delete Studentwhere Semester > 13;

update Studentset Semester= Semester + 1;

SnapshotSemantics1. Phase1:marktupleswhichareaffectedbytheupdate

2. Phase2:implementupdateonmarkedtuples

Otherwise,indeterministicexecutionofupdates:

deletefrom requireswhere prerequisitein (select follow-up

from requires);

delete from requrieswhere Prerequisite in (select Follow-up

from requires);

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Views:LogicalDataIndependence

View 1 View 2 View 3

Relation 1 Relation 2 Relation 3

Logicaldata independence

Physicaldata independence

DefiningaView

CREATE VIEW <NAME_OF_VIEW>AS<SQLQUERY>;

Thenyoucanuse<NAME_OF_VIEW>justlikeatable.

orig dest price

PEK ZRH 100

PEK MUC 10

MUC ZRH 20

MUC LUX 30

PEK SFO 1000

SFO ZRH 1000

Flight(orig,dest,price)CREATE VIEW FlightFromPEK ASSELECT *FROM FlightWHERE orig=PEK;

SELECT*FROMFlightFromPEKWHEREdest =ZRH; What’stheoutput?

That’sit.Whydoweevenneedthis?

Application1:Privacy

orig dest price

PEK ZRH 100

PEK MUC 10

MUC ZRH 20

MUC LUX 30

PEK SFO 1000

SFO ZRH 1000

Flight(orig,dest,price) CREATE VIEW FlightFromPEK ASSELECT *FROM FlightWHERE orig=PEK;

ThisusercanneverknowtheflightsfromMUC->ZRH.

(Informationgetsprotected,IfforsomereasonMUC->ZRHisa“secret”flight)

Application1:Usability

orig dest price

PEK ZRH 100

PEK MUC 10

MUC ZRH 20

MUC LUX 30

PEK SFO 1000

SFO ZRH 1000

SELECT*FROMFlightFromPEKWHEREdest =ZRH;

SELECT*FROMFlightWHEREdest =ZRHandorig=PEK;

Youwillseemoresignificantsavingssoon!

Views...

for privacy

create view testView asselect Legi, Nr, PersNrfrom tests;

Views...

for simpler queriescreate view StudProf (Sname, Semester, Title, Pname) as

select s.Name, s.Semester, l.Title, p.Namefrom Student s, attends a, Lecture l, Professor pwhere s.Legi=a.Legi and a.Nr=l.Nr and

l.PersNr= p.PersNr;

select distinct Semesterfrom StudProfwhere PName=`Alonso ‘;

Viewsforis-arelationships

create table Employee(PersNr integer not null,Name varchar (30) not null);

create table ProfData(PersNr integer not null,Level character(2),Room integer);

create table AssiData(PersNr integer not null,area varchar(30),Boss integer);

Basetables

create view Professor asselect *from Employee e, ProfData dwhere e.PersNr=d.PersNr;

create view Assistant asselect *from Employee e, AssiData dwhere e.PersNr=d.PersNr;

create table Professor (PersNr integer not null,Name varchar (30) not null,Level character (2),Room integer);

create table Assistant(PersNr integer not null,Name varchar (30) not null,area varchar (30),Boss integer);

create table OtherEmps(PersNr integer not null,Name varchar (30) not null);

Basetables

create view Employee as(select PersNr, Name

from Professor)union

(select PersNr, Namefrom Assistant)

union(select*

from OtherEmps);

Howaviewgetsevaluatedq QueryRewriting

orig dest price

PEK ZRH 100

PEK MUC 10

MUC ZRH 20

MUC LUX 30

PEK SFO 1000

SFO ZRH 1000

SELECT*FROMFlightFromPEKWHEREdest =ZRH;

SELECT*FROM(SELECT *FROM FlightWHERE orig=PEK)TWHERET.dest =ZRH;

SELECT*FROMFlightTWHERET.orig=PEKandT.dest =ZRH;

Let’sseesomerealexamples

cName state

College(cName,state,enroll)

sID sName GPA

1 A 3.9

2 B 3.6

3 C 3.5

4 D 3.9

5 E 2.9

6 F 3.8

Student(sID,sName,GPA)

sID cName major decision

1 S CS Y

1 S EE N

1 B CS Y

1 C EE Y

2 B BIO N

3 M BIOE Y

3 C BIOE N

3 C CS Y

3 C EE N

Apply(sID,cName,major,decision)

GraphRepr.

cName state

sID sName GPA

1 A 3.9

2 B 3.6

3 C 3.5

4 D 3.9

5 E 2.9

6 F 3.8

1 S CS Y

1 S EE N

1 B CS Y

1 C EE Y

2 B BIO N

3 M BIOE Y

3 C BIOE N

3 C CS Y

3 C EE N

SELECT *FROMCsaccept;

cName state

sID sName GPA

1 A 3.9

2 B 3.6

3 C 3.5

4 D 3.9

5 E 2.9

6 F 3.8

1 S CS Y

1 S EE N

1 B CS Y

1 C EE Y

2 B BIO N

3 M BIOE Y

3 C BIOE N

3 S CS Y

3 C EE N

cName state

sID sName GPA

1 A 3.9

2 B 3.6

3 C 3.5

4 D 3.9

5 E 2.9

6 F 3.8

1 S CS Y

1 S EE N

1 B CS Y

1 C EE Y

2 B BIO N

3 M BIOE Y

3 C BIOE N

3 S CS Y

3 C EE N

SELECT*FROMCSberk WHERE

sID<3;

cName state

sID sName GPA

1 A 3.9

2 B 3.6

3 C 3.5

4 D 3.9

5 E 2.9

6 F 3.8

1 S CS Y

1 S EE N

1 B CS Y

1 C EE Y

2 B BIO N

3 M BIOE Y

3 C BIOE N

3 S CS Y

3 C EE N

DROP VIEWCSaccept?

q Canweupdateaview?

Whatwewant…

R1,…Rn R1’,…Rn’

FindR1’,…Rn’suchthatV’isconsistentwithyour“updatequery”onV

Isthisalwayspossible?

Limitation1:Projection

1 S CS Y

1 S EE N

1 B CS Y

1 C EE Y

2 B BIO N

3 M BIOE Y

3 C BIOE N

3 S CS Y

3 C EE N

Whatwouldhappenifwe

INSERTINTOCsacceptVALUES(2)

Limitation2:Aggregation

Whatwouldhappenifwe

UPDATEVSETv=v+1;

CREATEViewV(v)ASSELECTSUM(r)FROMR;

Notallarebadnews

R(r,c)

Whatwouldhappenifwe

DELETEFROMVWHEREv=5;

CREATEViewV(v)ASSELECTrFROMR;

UpdatableViews

Example view which is not updatablecreate view ToughProf (PersNr, AvgGrade) as

select PersNr, avg(Grade)from testsgroup by PersNr;

update ToughProf set AvgGrade= 6.0where PersNr = 4711;

insert into ToughProfvalues (4711, 6.0);

SQL tries to avoid indeterminism.

Whataboutthis?

create view ToughProf (PersNr, AvgGrade) asselect PersNr, avg(Grade)from testsgroup by PersNr;

delete ToughProfwhere PersNr = 4711;

ViewsandUpdates

Example view which is not updatablecreate view LectureView as

select Title, CP, Namefrom Lecture l, Professor pwhere l.PersNr = p.PersNr;

insert into LectureViewvalues (`Nihilismus‘, 2, `Nobody‘);

There are scenarios in which the „insert“ is meaningful. There are scenarios in which SQL would have to guess. SQL is conservative and does not allow any scenario.

ViewsandUpdatesinSQL

q ASQLview is updatable iffØ Theview involves only one base relationØ Theview involves the key of that base relationØ Theview does NOTinvolve aggregates,group by,or duplicate-elimination

All views

Updatable views (theoretically)

Updatable views in SQL

Recursion

SQLWeSawsofarq SELECT… FROM… WHEREq Aggregationq Subqueryq NULLq SyntaxSugarsq Views

Aretheyenough?

ExampleofLimitation

parent child

A B’

C D’

ParentOf(parent,child)

Q1:Whoistheparent ofD?

SELECT parentFROM ParentOfWHERE child=D

parent??

Q2:Whoisthegrandparent ofD?SELECT p2.parentasgparentFROM ParentOf p1,ParentOf p2WHERE p1.child=DAND

p1.parent=p2.child

gparent??Q3:Whoisthegreatgrandparent ofD?

SELECT p3.parentasggparentFROM ParentOf p1,ParentOf p2,ParentOf p3WHERE p1.child=DAND

p1.parent=p2.childANDp2.parent=p3.child

ggparent??

Q4:WhoarealltheancestorsofD?

Howmanyqueriesdoweneed?(=Depthofthetree)

WhatiftheDepthisnotknown?

AnotherExample

orig dest price

PEK ZRH 100

PEK MUC 10

MUC ZRH 20

MUC LUX 30

PEK SFO 1000

SFO ZRH 1000

Flight(orig,dest,price)

SFOPEK

Q1:WhatisthecheapestpriceofdirectflightfromPEKtoZRH?SELECTmin(price)FROM FlightWHERE orig =PEKANDdest =ZRH

price??

Q2:Whatisthecheapestpriceof1-stopflightfromPEKtoZRH?

SELECTmin(f1.price+f2.price)FROM Flightf1,Flightf2WHERE f1.orig=PEKANDf2.dest=ZRH

ANDf1.dest=f2.orig

price??

Q3:Whatisthecheapest priceFromPEKtoZRH?

HowtowritethisinSQL?

Limitsoftherelationalmodelq Recursionisanaturaloperationinprogramming

q Itisalsoanaturalwaytosearchsomedatamodelsbutnottherelationalmodel

q RecursionispossibleinSQL(butcomplexandinvolved)

q Considergraphdatabases…q …anexcursionintomoderndataprocessing.

Friendsq Alotofdatainsocialmediaisagraph:

Ø FriendsØ LikesØ RecommendsØ CommunicatesØ ContactlistsØ …

q Processingsuchdatainvolvesgraphtraversals,DFSandBFS,graphisomorphism,…

Weneedsomethingnew.

parent child

A B’

C D’

ancesterC

ancesterCB

ancesterCBA

Ancester1 Ancester2 Ancester3

SELECTp2.parentFROMAncester1p1,ParentOf p2WHEREp1.ancester=p2.child

SELECTparentFROMParentOfWHERED=child

1.Startingpoint

2.Samequeryagainandagain

3.Untilnochanges

WITH(DB2/SQL99)

ancesterC

ancesterCB

ancesterCBA

1.Startingpoint

2.Samequeryagainandagain(andUNIONtheresult)

3.Untilnochanges

WITHRAS

(basequeryUNIONrecursivequery)

<queryinvolvingR(andothertables)>

WITHAncesterOfD(ancester)AS(SELECTparentFROMParentOf WHERED=child

UNIONSELECTp2.parentFROMAncesterOfD p1,

ParentOf p2WHEREp1.ancester=p2.child)SELECT*FROMAncesterOfD;

UNIONvs.UNIONALL

ancesterC

ancesterCB

ancesterCBA

1.Startingpoint

2.Samequeryagainandagain(andUNIONtheresult)

3.Untilnochanges

WITHRAS

(basequeryUNIONrecursivequery)

<queryinvolvingR(andothertables)>

WITHAncesterOfD(ancester)AS(SELECTparentFROMParentOf WHERED=child

UNIONSELECTp2.parentFROMAncesterOfD p1,

ParentOf p2WHEREp1.ancester=p2.child)SELECT*FROMAncesterOfD;

MoreAbstractInterpretation

parent child

A B’

C D’

{(P,D)|(p,c)Î ParentOf L p = P L c = D}{(P,D)|(p1,c1),(p2,c2)Î ParentOf L p1=c2 L p2 = P L c1 = D}{(P,D)|(p1,c1),(p2,c2),(p3,c3)Î ParentOf L p1=c2 L p2=c3 L p3 = P L c1 = D}…

TransitiveClosure ofRelationParentOf Whyisitcalledtransitiveclosure?

EvenMoreAbstractDefinition

R(A,B)

1 2 3 4 5 6

transA,B(R)= {(a,b) | $k Î IN ($G1, ..., Gk Î R (

G1.A= G2.B L

Gk-1.A= Gk.B L

G1.A= a L

Gk.B= b))}

HowtowritethisinSQL?

R(A,B)1 2 3 4 5 6

transA,B(R)= {(a,b) | $k Î IN ($G1, ..., Gk Î R (

G1.A= G2.B L

Gk-1.A= Gk.B L

G1.A= a L

Gk.B= b))}

WITHTransR(B)AS

(SELECT BFROM RWHEREA=“a”UNIONSELECT p2.BFROMTransR p1,Rp2WHERE p1.B=p2.A)

SELECT*FROMTransR ;

select Bfrom Rconnect by A = prior Bstart with A = (select B

from R where A=“a”));

OracleCONNECTBYClause

Example

select l1.prerequisite

from requires l1, requires l2, Lecture lwhere l1.Follow-up = l2.prerequisite and

l2.Follow-up = l.Nr andl.Title=`Databases´;

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Q:Allprerequisitesclassof“Database”

Doesthisanswerthequery?

connect by Clause (Oracle)

select Titlefrom Lecturewhere Nr in (select prerequisite

from requiresconnect by follow-up = prior prerequisitestart with follow-up = (select Nr

from Lecturewhere Title = ... ));

Recursion inDB2/SQL99

with TransLecture (First, Next)as (select prerequisite, follow-up from requires

union allselect t.First, r.follow-upfrom TransLecture t, requires rwhere t.Next= r.prerequisite)

select Title from Lecture where Nr in(select First from TransLecture where Next in

(select Nr from Lecturewhere Title = `Der Wiener Kreis´) )

Will“WITH”AlwaysTerminate?

WITHRECURSIVER(r)AS

(SELECT 1UNION

SELECT rFROM R)SELECT *FROM R

WITHRECURSIVER(r)AS

(SELECT 1UNION

SELECT r+1 FROM R)SELECT *FROM R

WITHRECURSIVER(r)AS

(SELECT 1UNION

SELECT r+1 FROM R)SELECT *FROM RLIMIT10;

PostgreSQLSyntax

Howaboutthisone?

WITHRECURSIVER(r)AS

(SELECT 1UNION

SELECT r+1 FROM R)SELECTmin(r)FROM RLIMIT10;

PostgreSQLSyntax

Howaboutthisone?

WITHRECURSIVER(r)AS

(SELECT 1UNION

SELECT r+1 FROM RWHERE r<20)SELECTmin(r)FROM RLIMIT10;

PostgreSQLSyntax

Howaboutthisone?

WITHRECURSIVER(r)AS

(SELECT 1UNIONALL

SELECT*FROMR)SELECT *FROMR;

PostgreSQLSyntax

WITHRECURSIVER(r)AS

(SELECT 1UNION

SELECT*FROMR)SELECT *FROMR;

Example1

parent child

A B’

C D’

WITHAncestor(a,d)AS(SELECT parentAS a,childAS dFROM ParentOf

UNIONSELECT Ancestor.a,ParentOf.child AS dFROM Ancestor,ParentOfWHERE Ancestor.d =ParentOf.parent)

SELECT aFROM AncestorWHERE d=“D”.

WhoarealltheancestorsofD?

SELECT aFROM AncestorWHERE d=“B”.

SELECT aFROM AncestorWHERE d=“A”.

Example2

parent child

1 $100

Employee(id,salary)

mid eid

Manager(mid,eid)

name mgrid

Project(name,mgrid)

Example2

parent child

1 $100

Employee(id,salary)

mid eid

Manager(mid,eid)

name mgrid

Project(name,mgrid)

PostgreSQLSyntax

Example2

parent child

1 $100

Employee(id,salary)

mid eid

Manager(mid,eid)

name mgrid

Project(name,mgrid)

PostgreSQLSyntax

Example2

parent child

1 $100

Employee(id,salary)

mid eid

Manager(mid,eid)

name mgrid

Project(name,mgrid)

PostgreSQLSyntax

Example3

D-INFK,ETHZurich,DataModelingandDatabases 70PostgreSQLSyntax

orig dest airline price

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

Flight(orig,dest,airline,price)

Drawgraphontheboard

Example3

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

Example3

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

Example3

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

WhatifweonlycareaboutstartingfromA?

Example3

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

WhatifweonlycareaboutstartingfromA->B?

WHEREdest =“B”

Example3

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

YoucandosimilarthingsforB

Example3(Whatifthereisloop)

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

CMH PHX FT 80

Drawgraphontheboard

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

CMH PHX FT 80

Whatwillhappenifwerunthis?

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

CMH PHX FT 80

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

CMH PHX FT 80

max(total) Whatwillhappenifwerunthis?

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

CMH PHX FT 80

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

CMH PHX FT 80

max(total) Whatwillhappenifwerunthis?

A ORD UA 200

ORD B AA 100

A PHX SW 25

PHX LAS SW 30

LAS CMH FT 60

CMH B FT 60

A B JB 195

CMH PHX FT 80

max(total) Whatwillhappenifwerunthis?1000000000

Data Modeling and Databases Advanced SQL

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