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L06:SQL

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Announcements!

• Pleasepickupyournamecard- alwayscomewithyournamecard- Ifnobodyanswersmyquestion,Iwilllikelypickonthosewithoutanamecard orinthe

lastrow

• Pollsonspeed:weslowdownandhaveanotherSQLlecture(likelynoNoSQL)• Usetheanonymousfeedbackform• HW3 andlater:inteams

• Outlinetoday:- HW1 together- outerjoins,nulls

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SELECT cnameFROM Product P, Company WHERE country = 'USA' AND P.category = 'Gadgets' AND P.manufacturer = cname

Awordoncapitalization 302

Product (pname, price, category, manufacturer)Company (cname, stockprice, country)

Q:FindallUScompaniesthatmanufactureproductsinthe'Gadgets'category!

Myrecommendationforcapitalization

1.SQLkeywordsinALLCAPS,2.TablenameswithInitialCaps3.Columnnamesallinlowercase.

Moreinformation:http://blog.lerner.co.il/quoting-postgresql/ ,https://stackoverflow.com/questions/6331504/omitting-the-double-quote-to-do-query-on-postgresql

PostgreSQLtreatsallinlowercase.Exceptifyouwrite:createtable"Product"(…)ThiswillpreservecapitalizationoftablenameBut… youneedtoalwaysusequotations

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HW1

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BigIMDBschema(Postgres)

Actoridfnamelnamegender

Movieidnameyear

Directorsidfnamelname

Castspidmidrole

Movie_directorsdidmid

Genremidgenre

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QuizFindthefirst/lastnamesofallactorswhoappearedinbothofthefollowingmovies:KillBill:Vol.1andKillBill:Vol.2.

SELECT DISTINCT A.fname, A.lnameFROM Actor A, Casts C, Movie M1, Movie M2WHERE M1.name = 'Kill Bill: Vol. 1'

and M2.name = 'Kill Bill: Vol. 2'and M1.id = C.midand M2.id = C.midand C.pid = A.id

IMDB (postgres)

PictureSource:http://queryviz.com/online

L

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QuizFindthefirst/lastnamesofallactorswhoappearedinbothofthefollowingmovies:KillBill:Vol.1andKillBill:Vol.2.

IMDB (postgres)

SELECT DISTINCT A.fname, A.lnameFROM Actor A, Casts C, Movie M1, Movie M2, Casts C2WHERE M1.name = 'Kill Bill: Vol. 1'

and M2.name = 'Kill Bill: Vol. 2'and M1.id = C.midand M2.id = C2.midand C.pid = A.idand C2.pid = A.id

PictureSource:http://queryviz.com/online

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QuizFindthefirst/lastnamesofallactorswhoappearedinbothofthefollowingmovies:KillBill:Vol.1andKillBill:Vol.2.

IMDB (postgres)

SELECT A.id, A.lname, A.fname,FROM actor A, cast C, movie MWHERE M.id = C.mid

AND A.id = C.pidAND (M.name = 'Kill Bill: Vol. 1'

OR M.name = 'Kill Bill: Vol. 2')GROUP BY A.id, A.lname, A.fnameHAVING count(M.id) > 1

WhatifanactorplayedtworolesinKillBill1?

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Null Values

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3-valuedlogicexample

• Threelogicianswalkintoabar.Thebartenderasks:"Doallofyouwantadrink?"

• The1stlogiciansays:"Idon'tknow."• The2ndlogiciansays:"Idon'tknow."• The3rdlogiciansays:"Yes!"

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NullsinSQL

• Wheneverwedon'thaveavalue,wecanputaNULL

• Canmeanmanythings:- Valuedoesnotexists- Valueexistsbutisunknown- Valuenotapplicable- Etc.

• TheschemaspecifiesforeachattributeifitcanbeNULL(nullableattribute)ornot

• HowdoesSQLcopewithtablesthathaveNULLs? 243

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NullValues

• InSQLtherearethreeBooleanvalues:- FALSE,TRUE,UNKNOWN

• Ifx=NULLthen- ArithmeticoperationsproduceNULL.E.g:4*(3-x)/7- BooleanconditionsarealsoNULL.E.g:x='Joe'- aggregatesignoreNULLvalues

• Logicalreasoning:- FALSE=0 xANDy=min(x,y)- TRUE=1 xORy=max(x,y)- UNKNOWN=0.5 NOTx=(1– x)

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NullValues:exampleSELECT *FROM PersonWHERE (age < 25)

and (height > 6 or weight > 190)

Age Height Weight20 NULL 200NULL 6.5 170

Person

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NullValues:exampleSELECT *FROM PersonWHERE (age < 25)

and (height > 6 or weight > 190)

RuleinSQL:includeonlytuples thatyieldTRUE

Age Height Weight20 NULL 200NULL 6.5 170

Person

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NullValues:exampleSELECT *FROM PersonWHERE (age < 25)

and (height > 6 or weight > 190)

RuleinSQL:includeonlytuples thatyieldTRUE

Age Height Weight20 NULL 200NULL 6.5 170

SELECT *FROM PersonWHERE age < 25 or age >= 25

Person

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NullValues:exampleSELECT *FROM PersonWHERE (age < 25)

and (height > 6 or weight > 190)

RuleinSQL:includeonlytuples thatyieldTRUE

Age Height Weight20 NULL 200NULL 6.5 170

SELECT *FROM PersonWHERE age < 25 or age >= 25

Unexpectedbehavior

SELECT *FROM PersonWHERE age < 25 or age >= 25 or age IS NULL

TestNULLexplicitly

Person

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NullValuesandAggregates

gid val1 NULL1 NULL2 a2 a2 z2 z2 NULL3 A3 A3 Z

SELECT gid, MAX(val) maxv,MIN(val) minv, COUNT(*) ctr, COUNT(val) ctv, COUNT(DISTINCT val) ctdv

FROM TGROUP BY gidORDER BY gid

T

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?

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ctdv032

NullValuesandAggregates

gid val1 NULL1 NULL2 a2 B2 z2 z2 NULL3 A3 A3 Z

SELECT gid, MAX(val) maxv,MIN(val) minv, COUNT(*) ctr, COUNT(val) ctv, COUNT(DISTINCT val) ctdv

FROM TGROUP BY gidORDER BY gid

T

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gid123

maxvNULLzZ

ctv043

ctr253

minvNULLBA

NULLisignoredbyaggregatefunctionsifyoureferencethecolumnspecifically.Exception:COUNT!

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Inner Joinsvs. Outer Joins

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AlternaiveJoinSyntax

SELECT Item.name, Purchase2.storeFROM Item JOIN Purchase2 ON

Item.name = Purchase2.iName

SELECT Item.name, Purchase2.storeFROM Item, Purchase2WHERE Item.name = Purchase2.iNameSameas:

An"innerjoin":

Name CategoryGizmo GadgetCamera PhotoOneClick Photo

ItemName StoreGizmo WizCamera RitzCamera Wiz

ResultiName Store MonthGizmo Wiz 8Camera Ritz 8Camera Wiz 9

Purchase2

Item(name,category)Purchase2(iName,store,month)

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etext eid fid ftextOne 1 1 UnThree 3 3 TroisFour 4 4 QuatreFive 5 5 CinqSix 6 6 Siz

Illustrationfid fText1 Un3 Trois4 Quatre5 Cinq6 Siz7 Sept8 Huit

EnglisheText eidOne 1Two 2Three 3Four 4Five 5Six 6

French

SELECT *FROM English, FrenchWHERE eid = fid

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SELECT *FROM English JOIN FrenchON eid = fid

Sameas:

An"innerjoin":

"JOIN"sameas

"INNERJOIN"

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etext eid fid ftextOne 1 1 UnTwo 2 NULL NULLThree 3 3 TroisFour 4 4 QuatreFive 5 5 CinqSix 6 6 SizNULL NULL 7 SeptNULL NULL 8 Huit

Illustrationfid fText1 Un3 Trois4 Quatre5 Cinq6 Siz7 Sept8 Huit

EnglisheText eidOne 1Two 2Three 3Four 4Five 5Six 6

French

SELECT *FROM English FULL JOIN FrenchON English.eid = French.fid

SQLitedoesnotsupport"FULLOUTERJOIN"sL (but"LEFTJOIN")

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SELECT *FROM English JOIN FrenchON eid = fid

"FULLJOIN"sameas

"FULLOUTERJOIN"