sql: easy sql programming & database management for beginners, your step-by-step guide to...

EasySQLProgramming&DatabaseManagementForBeginners.YourStep-By-StepGuideToLearningTheSQLDatabase.

FelixAlvaro

Acknowledgments

Firstly,IwanttothankGodforgivingmetheknowledgeandinspirationtoputthisinformativebooktogether.Ialsowanttothankmyparents,mybrothersandmypartnerSilviafortheirsupport.

TableofContents

ChapterOne:SQLOverview-HistoryofSQL-UsesofSQL

-PeopleUsingSQL

ChapterTwo:TheDatabaseEssentials-DatabaseFundamentals-RelationalDatabaseFundamentals-DatabaseManagementSystemsChapterThree:TheSQLStructure

-SQLFundamentalFeatures-SQLCommandTypes-SQLiteDatabaseFeaturesandInstallationInstructions

ChapterFour:DataTypes-DefinitionofData-TypesofData-User-DefinedDataTypeChapter

Five:DataDefinitionLanguageStatements-CREATEStatement-ALTERStatement-DROPStatementChapter

Six:DataManipulationLanguageStatements-INSERTStatement-UPDATEStatement-DELETEStatement

ChapterSeven:DataQueryLanguageStatements-SELECTStatement-WHEREStatement-ORDERBYandGROUP

BYStatementsChapterEight:TransactionalControlCommands-COMMITCommand-ROLLBACKCommand-SAVEPOINT

CommandChapterNine:DatabaseViews-DefiningViews-CreatingViews-DroppingViewsChapterTen:

EnhancingDatabaseDesigns-AssigningPrimaryandForeignKeys-UnderstandingIndexes-NormalizingDatabasesChapterEleven:DatabaseAdvanceTopics

-Cursors-Triggers-ErrorsRecap+FinalWords-RecapandFinalwords-Checkoutmyotherbooks

©Copyright2016byD.A.Alvaro-Allrightsreserved.Thisdocumentisgearedtowardsprovidingexactandreliableinformationinregardstothetopicandissuecovered.Itisnotlegaltoreproduce,duplicate,ortransmitanypartofthisdocumentineitherelectronicmeansorinprintedformat.Recordingofthispublicationisstrictlyprohibited.

IntroductionHithere!ThankyousomuchfordownloadingthiseBookinSQL

ProgrammingandDatabaseManagementforBeginners.Iassureyouthatyouhavemadeawisedecisionininvestinginyourskillsasadatabaseprofessional.ThiseBookwillteachyouvitalinformationonthefundamentalsofdatabaseprogrammingandmanagementusingoneofthepowerfulsoftwaretools–theSQLlanguage.IamFelix,whoalsostartedasasimpleanalystandnowprogressingintobecomingadatabasescientist.ThroughtheguidanceofthiseBook,youwillhaveabetterunderstandingofthecountlessopportunitiesthatthisSQLlanguagecanbringyou.Iwillbepresentingyoustep-by-stepinstructionsinlearningtheessentialskillsofthisreliabledatabasesoftware.

Atfirst,IdidnotrealizehowimportantitisforonetocomprehendSQLifthereareotherprogramapplicationsyoucanuse,suchasMicrosoftExcel,toprocessandpresentinformation.WhenIstartedresearchingforthevalueofSQL,ItoldmyselfthatifIcontinueembarkingonthisfieldthenIwillnotjustbepresentinginformationbutanalyzingdataaswell.Afterdownloadingandinstallingthesoftware,IhavefoundoutthatitisnotthatchallengingtostudySQLprogrammingafterall!Takingthatfirststeptounderstandingthebasicdatabaseconceptswillleadyoutoexpandingyourknowledgeinbecomingoneofthemostsought-afterITprofessionals.

Thecurrenttrendininformationtechnologyistobemoredigital,whichentailsmanipulatingdatabases.ThisiswhereSQLcomesinplace–asoftwarelanguagethatispowerfulyetsimple,flexible,portableand,mostofall,integratedintonumerousdatabaseapplications.Decidingtobecomeadatabaseprofessionalwilldefinitelypromiseyouasecuredjobwithapotentialhighremuneration.Ontheaverage,asimpledatabaseanalystintheUnitedStatesearnsanannualsalaryofaround$92,000USD.

Tostartyourjourneyinthisfieldofdatabaseprogrammingandmanagement,letthiseBookserveasyourinitialguideineducatingyourselfwiththebasicsofSQL.Iwillprovideyouanoverviewofhowthelanguagestarted,thevariousfeaturesofthesoftwareanditsenvironment,thedifferentcommandsandfunctions,theavailableerror-handlingtools,someadvancedtopicsandmanymore!MyultimateaimisforyoutoappreciatethepotentialsofSQLandgrasptheprogrammingconceptsinacoolway.Sowhatareyouwaitingfor?Letusgetstarted!

ChapterOne:SQLOverview

InthischapteryouwilllearnabriefbackgroundonhowandwhySQLcameintoexistence.GainingknowledgeonthehistoryofthiscomputerlanguagewillhelpyouunderstanditsimportancetomostITprofessionalswhofocusonthefieldofdatamanipulation.YouwillalsohaveanideaonhowtomaximizethepotentialsofSQLintheever-changingworldofInformationTechnology.

Thecurrenttrendinmostbusinessestodayistoinvestintechnologythatwillgatherdatainthemostefficientandeffectiveway.However,gatheringinformationisonlythestartoftheextensiveprocessofdatamanipulation.Companies,especiallymultinationalones,requireexpertswhopossesstheskillsofanalyzing,presenting,managingandstoringdata.Inotherwords,theyneedtousecomputerprogramsthatwilltransformrawcompanydatatousefulinformation.Now,thankstoStructuredQueryLanguage,orsimplySQL,thatbroughtaboutsuchtransformationinaccessingandmanipulatingdatainaverymeaningfulway.

HistoryofSQL

Pronouncedasees-que-ellorsee’qwl,SQLisacomputerlanguageinitiallyinventedbyanAmericanmultinationaltechnologyandconsultingcompanyknownasIBM(InternationalBusinessMachinesCorporation)wayback1970susingDr.E.F.Codd’spaperon“ARelationalModelofDataforLargeSharedDataBanks”fortheprototypedesign.ItwasoriginallycalledSEQUEL(StructuredEnglishQUEryLanguage)thathandledqueriesonthecollectionandorganizationofdata-orsimplyknownasadatabase.Morefeatureswereaddedtothecomputersoftwaretoimproveitsperformance,likebuildingandmanagingdatabasesecurity,amongothers.WhenIBMresearcherslearnedthatthereisanothercompanythathadthesame“Sequel”trademark,theyrenameditto“S-Q-L”(presentlyexpandedasStructuredQueryLanguage).

Sinceitwasfirstreleasedtothepublic,SQLalreadyhadmanyversions.In1979,RelationalSoftware,Incorporated(whichlaterbecametheOracleCorporation)releasedORACLE,thefirstSQLproduct.Now,asthedemandforcomputersthatmanagedatahasincreased,themoreSQLhasbecomeanindustrystandardinthefieldofInformationTechnology.SuchformalstandardissetandmaintainedbytheInternationalStandardsOrganization,orsimplyknownasISO.Itwason1986,basedonIBM’simplementation,thatSQLhasbeenrecognizedasthestandardlanguageindatabasecommunication.Thefollowingyear,ISOacceptedANSISQLastheinternationalstandard.ANSIstandsforAmericanNationalStandardsInstitute,whichisanorganizationthatapprovescertainstandardsinvariousUSindustries.Manyrevisionsofthestandardsfollowed,suchasin1992(SQL-92)andin1999(SQL-99).ThelatestoneisnowcalledSQL-2011,whichwasofficiallyreleasedinDecember2011.

UsesofSQL

Thecorporateworldisnowshiftingfrommerelyproducingproductsandprovidingservicestoinvestingindigitaltechnologiesthathandlevastamountsofdata,tobetransformedtomeaningfulpiecesofinformationthatwillgeneratemoreprofitableincomeforthecompany.ThisistheprimaryobjectiveofSQL–toaccessandmanipulatedatathatwillfurtherleadtobusinessinsights.Thisflexiblecomputerlanguagehasbeenthemostwidelyusedcommunicationtoolinhandlingdatabases(specificallyrelationaldatabasesthatwillbefurtherdiscussedinChapter3ofthisbook).

Trytoimaginethatyouaregoingtoaforeigncountryforavacation.Youmayneedtolearnthatcountry’slanguagetofindyourwayaroundasyouexplorethenewplace.Whenyoutryasksomeonefordirections,whoislocaltothatplaceandonlyspeaksthecountry’slanguage,thensurelyyouwillhaveahardtimeunderstandinghim.Inthisscenario,theforeignlandwillbeyourdatabaseinwhichyouneedtoseekinformationwhileSQListhelanguagethatyouwillusetogetwhatyouneedfromthedatabase.

Fromtimetotime,youwillencounterthetermquery,whichisalsoapartoftheabbreviationofSQL.QueryisbasicallythequestionwrittenusinganSQLstatementthatisbeingaskedfromthedatabase.SQLthenretrievestheneededinformationwhenanyofthedatainthedatabasemeetstherequirementsoftheconditionsofthegivenquery.Soinreal-lifeapplications,suchasanonlinestore,whenyouexecuteyourqueryforaspecificitembyenteringyoursearchcriteria,SQLprogrammingusuallytakesplaceinthebackgroundtomanagethedatabaseconnections.Youareactuallytellingthedatabase,throughthehelpofSQL,whatinformationyouwanttoseeandhowyouwantittobepresentedtoyou.

PeopleUsingSQL

SQLisnotonlyapplicableforITprofessionalsorgeekswhopossessremarkableprogrammingskills.Withthegrowingcorporateworldoftoday,non-ITpersonnelsuchasbusinessmenandmanagers,canalsobenefitfromlearningthesemanticsofSQL.Thisisbecausethecomputerlanguageenablesthemtounderstandtheinsandoutsoftheirbusinessesusingthedatathatdriveseverycompany.Moreover,itopensseveralcareeropportunitiesintheanalytical,managerial,strategicorresearchfields-forthosewhowanttostep-upfromtheircurrentpositions.OntheITfield,SQLknowledgecanleadtomorechallengingrolessuchasdatabasedesigners,administratorsorscientists,systemsengineers,projectmanagersandsoftwaredevelopers,amongothers.

InthischapteryouhavelearntanoverviewofSQL–itshistory,itsprimarypurposewhyitwascreatedandthosewhowillprofitfromlearningthispowerfuldatabasesoftware.Inthenextchapteryouwilllearntheessentialsofdatabase,whichistheprimaryreasonwhySQLwasdesignedinthefirstplace.

ChapterTwo:TheDatabaseEssentials

BeforeyoustartlearningthetechnicalitiesofSQLasacomputerlanguage,thischapterwilldiscussfirstwhatadatabaseisanditsfundamentalcharacteristics.Youwillalsobeinformedwhythebusinessworldisnowdriventogatherandmanipulatedatatobringforthmoreprofitableincome.

DatabaseFundamentalsTherearemanywaysonhowtodefineordescribewhatadatabaseis.Insimpleterms,itcanbedefinedasacollectionofitemsthatcanexistoveralongperiodoftime.Thinkofacallingcardholderasadatabasethatcontainsbusinesscardswithdifferentinformationofpeoplethatyouknow(e.g.person’sname,jobtitle,companyname,contactnumber).Anotheroneisaprintedtelephonedirectory(morepopularlyknownastheyellowpages)thatcontainsthename,phonenumberandaddressoftheregisteredresidentslivinginaparticulararea.

Somedefinedatabasemoreprofessionally,notjustacollectionofdata.Itisdescribedasanorganizedtoolcapableofkeepingdataorinformationthatyoucanretrieveinaneffectiveandefficientwaywhentheneedarises.Itcanalsobemorestrictlydefinedasaself-describingcollectionofobjectsthatareintegratedtooneanother.Whenyoucreaterepresentationsofthesephysicalorconceptualobjectsthentheywillbecalledrecords.Fromthepreviousexampleofyourcallingcardholder,ifyouwishtokeeptrackofyourbusinesscontactsthenyouhavetoassigneachbusinesscardaspecificrecord.Everyrecordcontainsmultipleinformationordata,suchasindividualname,jobtitle,companynameandaddress,phonenumberandmorethatyouwillnowcalltherecord’sattributes.

Adatabasedoesnotonlycontainthedatathatyouneed,butalsowhatyoucallitsmetadata.Thisistheinformationthatdefinesordescribesthedata’sstructurewithinthegivendatabase(thatiswhyitwasdefinedearlierasaself-describingentity),storedinaregioncalleddatadictionary.Thus,dataretrieval

willbefasterifyouknowhowinformationisarrangedandstored.Furthermore,relationshipsexistamongthedataitemssincetheyareintegratedtooneanother.Checkthefollowingfigureforasampleillustrationofwhatadatabaseis.

Whetheradatabasecontainsasimplecollectionofafewrecordsoramassivesystemcomposedofmillionsofrecords,itcanbecategorizedintothreetypes:personal,workgroupordepartmental,andenterprise.Eachcategoryischaracterizedbythedatabasesize,themachinerysizeintowhichthedatabaserunsandhowbigtheorganizationthatmanagesit.

PersonalDatabase–Thisisconceptualizedanddesignedbyasinglepersononastand-alonecomputer.Itsdatabasestructureisrathersimpleandthesizeisrelativelysmall.Forexample,yourpersonalelectronicaddressbook.Workgroup/DepartmentalDatabase–Thisisdesignedandcreatedbyindividualsofasingleworkgroupordepartmentwithinacertainorganization.Thedatabasestructureislargerandmorecomplex,ascomparedtothepersonalcategory,whichisalsoaccessedbymultipleusersatthesametime.EnterpriseDatabase–Amongthethreecategories,thistypeisconceptualizedandcreatedtohandletheentireflowofinformationofverylargeorganizations.Thus,thedatabasedesigninvolvesfarmore

complexstructures.

RelationalDatabaseFundamentalsTakingthediscussionfurtherintoamoretechnicalaspect,arelationaldatabaseisanentityconsistingoflogicalunitsknownastables.ThisrelationaldatabasemodelwasfirstformulatedbyDr.E.F.Coddin1970.Howthetablesarerelatedtoeachotherdefinestheirrelationships.Inthisscenario,dataissimplifiedintosmalleryetmorelogicalandmanageableunitsthatoptimizethedatabaseperformance.Thefollowingfigureshowsanillustrationonhowthevariouscomponentsofarelationaldatabaseareconnectedtoeachother.

Atableconsistsofrowsandcolumnsthatstoredata.Inarelationaldatabase,thesetablesarerelatedtooneanotherimprovingthedataretrievalprocesswhenaqueryissubmittedbytheuser.Foryoutoclearlypictureoutthisidea,converttheinformationfoundonthecallingcardholderintoaspreadsheetlikeaMicrosoftExcelfile.Assumethattheseareyourcontactsfromcompaniesthathaveorderedproductsandservicesfromyourbusiness.YouwillhaveatleastaCUSTOMERTABLE(containingallimportantinformationaboutyourcontacts)similartothefollowing:

CUSTOMERID

NAME POSITION COMPANY STATE CONTACTNO

KathyAle

President TileIndustrial

TX 3461234567

2 KevinLord

VP BestTooling

NY 5181234567

3 KimAsh

Director CarWorld CA 5101234567

4 AbbyKarr

Manager WestMart NV 7751234567

YouwillalsohaveanORDERTABLEthatwillstoreinformationsuchasorderID,date,quantityandmore.Checkthefollowingtable:

ORDERID

ORDERDATE

CUSTOMERID

PRODUCTID

ORDERQTY

1 2016-05-23 1 4 3002 2016-09-09 1 5 1003 2016-02-17 3 2 1504 2016-05-12 2 2 500

Asyoucansee,eachtablelookslikeanarrayofrowsandcolumns.ReferringtotheCUSTOMERTABLE,arowisalsocalledarecordoratuplethatholdsinformationforasinglecustomer.Ontheotherhand,acolumnholdsasingleattributeofthecustomer(i.e.,name,jobtitleorposition,companynameandaddress,contactnumber).Itisalsoself-consistent,meaningitcontainsthesametypeofdataineveryrow.Soifacolumncontainsthenameofyourcustomerinthefirstrow,thenthesucceedingrowswillhavetoshowthenamesofyourothercustomers.Thereisalsonosignificancewhichroworcolumnwillappearfirstandwhichwillbenext,sincethereisnoparticularorganizationthatisfollowed.Lookingatbothtables,youwillnoticethateachoneofthemhasacolumnthatcontainsthesamedatavalue–CUSTOMERID.Thisisnowcalledthecommonkey,whichlinksthetablestooneanotherinarelationaldatabase.Theexistenceofthecommonkeysmakesitpossibletomergedatafrommultipletablesinformingalargersetofdataentity.

Therelationbetweenthetwotablesconsistsofatwo-dimensionalarrayofdatastoredinrowsandcolumns.Theintersectionofarowandacolumniscalledacell.Eachcellcontainssinge-valuedentriesandeachrowisunique.Thus,eachcellhasonlyonevalueandnoduplicaterows.GoingbacktotheCUSTOMERandORDERTABLES,willbeabletocreatethefollowingrelationbyaddingtheCUSTOMERNAMEthatcorrespondstothegivenCUSTOMERID:

ORDERID

CUSTOMERID

CUSTOMERNAME

1 1 KathyAle2 1 KathyAle3 3 KimAsh4 2 KevinLord

Youwillseethatthereisnoemptycell.OneparticularorderreferencedbytheORDERIDisassociatedtoaparticularcustomer,indicatedbytheCUSTOMERIDandCUSTOMERNAME.TherearenotwocustomershavingthesameORDERID.Thatiswhy,therewillbenotworowsthatareexactlyidentical.

DatabaseManagementSystemsAdatabasemanagementsystem,orsimplyDBMS,isanimportantprogrammingtoolthatconsistsofasetofprogramsthatdefine,manageandprocessdatabasesandallapplicationsassociatedtothem.Throughthis,youareabletobuildastructureandoperateonthevaluabledatathatthedatabaseholdsinaveryefficientway.TherearetwomaintypesofusersthatworkonDBMS–theconventionaluserwhoretrievesormodifiesdataandtheadministratorwhoisresponsibleformaintainingthestructureofthedatabase.

ThefollowingarethekeyfeaturesofaDBMS:

AllowsthecreationofnewdatabasesandtheirdatastructuresAllowsdataqueryandmodificationusinganappropriateprogramminglanguageAllowsthestorageofvastamountsofdataoveralongperiodoftime

Enablesdatabaserecoveryintimesoffailure,errororintentionalmisuseControlsdataaccessfrommanyusersatonce

Itwasduringthelate1960swhenthefirstcommercialDBMSappeared.Itevolvedfromfilesystemsthatbasicallyprovideddatastorageforoveracertainperiodoftime.Thoughsuchsystemswerecapableofstoringtremendousamountofdata,computerprofessionalsstillhavetofaceproblemsofdatalossandaninefficientinformationretrievalsystem.Therewerealsoissuesoncontrolaccesswhereerrorsoccurwhentwousersmodifythesamefileatthesametime.Someexamplesoftheseapplicationsareairlinereservationsystems,bankingsystemsandcorporaterecordkeepingsystems,amongothers.

Withtheadvancementoftechnologyinthemarkettoday,youcanfindnumerousprogramsthatwillbesuitableforyourDBMSrequirements.Thereareapplicationsthatrunonasmallscalelevellikeyourpersonalcomputerortablet.Somearebuilttorunonalargeandpowerfulequipment,likethosebeingusedbymultinationalcompanies.Nevertheless,theon-goingtrendisforDBMStobeexecutedonmultipleplatformsormachines(whetherlargeorsmall)thatareinterconnectedtooneanother,forminganimmensescalablenetwork.ITexpertshavealsofoundwaysonhowstoredatausingInternettechnologyinpowerfuldatacentersormorepopularlyknownasclouds.Thiscloudcanbepublicentity(managedbyalargecompanylikeMicrosoftorGoogle)oraprivateone(maintainedandstoredviatheintranetwithinanorganization).

Inthischapteryouhavelearnttheessentialfeaturesofadatabaseandhowittransformstobecomearelationaldatabase.Also,youhadanoverviewofthehistoryandcharacteristicsofdatabasemanagementsystems.InthenextchapteryouwilllearnthefundamentalstructureoftheSQLlanguageanditscomponents.

ChapterThree:TheSQLStructure

InthischapteryouwilllearnthefundamentalfeaturesoftheSQLlanguageandanoverviewofitsprogrammingaspect.Inaddition,youwillbepresentedwithastep-by-stepinstructiononwhereandhowtodownloadSQLite,aversionoftheSQLsoftwarethatwillbeusedallthroughoutthediscussionofthise-Book.

SQLFundamentalFeaturesSQLisaflexiblecomputerlanguagethatyoucandeployindifferentwaystocommunicatewithrelationaldatabases.Thissoftwarehassomedistinctfeaturesthatdifferentiatesitfromotherprogrammingapplications.Firstandforemost,SQLisanonprocedurallanguage.Mostcomputerprograms(e.g.,C,C++andJava)solveproblemsbyfollowingasequenceofcommandsthatiscalledaprocedure.Inthiscase,onespecificoperationisperformedafteranotheruntiltherequiredtaskhasbeenaccomplished.Theflowofoperationcaneitherbealinearsequenceoraloopingone,dependingonwhattheprogrammerhadspecified.ThisisnotthesameforSQL.Inusingthisapplication,youwilljusthavetospecifytheoutputthatyouwant,nothowyouwanttogeneratetheoutput.FromtheCUSTOMERTABLE,ifyouwanttocreateaseparatelistofcontactswhosecompanyarelocatedinTexasthenyouhavetoretrievetherowswheretheSTATEcolumncontains“TX”asitsvalue.InwritingtheSQLcommand,youdon’thavetoindicatehowtheinformationshouldberetrieved.Itistheprimaryroleofthedatabasemanagementsystemtoexaminethedatabaseanddecidehowtogeneratetheresultsyouwanted.

LearningtheSQLsyntaxislikeunderstandingtheEnglishlanguagestructure.Itscommandlanguage,comprisedofalimitednumberofstatements,performsthreeprimarydatafunctions-definition,manipulationandcontrol.TheSQLprogramminglanguagealsoincludesreservedwordsthatareonlytobeusedforspecificpurposes.Thus,youcannotusethesewordsasnamesforvariables,tablesandcolumns;orinanyotherwayapartfromtheirintendeduse.

BelowaresomeofthemostcommonreservedwordsinSQL:2011.

ABS ALL ALLOCATE ALTER AND ANYARE ARRAY AS AT AVG BEGIN

BETWEEN BINARY BOOLEAN BOTH BY CALLCASCADED CASE CEILING CHAR CHARACTER CHECKCLOSE COLLATE COLLECT COLUMN COMMIT CONDITION

CONNECT CONSTRAINT CONVERT COUNT CREATE CURSORCYCLE DATE DAY DEALLOCATE DEC DECIMAL

DECLARE DEFAULT DELETE DESCRIBE DISCONNECT DISTINCTDOUBLE DROP DYNAMIC EACH ELEMENT ELSEEND ESCAPE EVERY EXCEPT EXECUTE EXISTS

EXTERNAL EXTRACT FALSE FETCH FILTER FLOATFLOOR FOR FOREVER FREE FROM FULL

FUNCTION FUSION GET GLOBAL GRANT GROUPGROUPING HAVING HOLD HOUR HOURS IDENTITY

IN INNER INOUT INSERT INT INTEGERINTERSECT INTERVAL INTO IS JOIN KEEPLANGUAGE LARGE LEAD LEFT LIKE LOCALLOWER MATCH MAX MEMBER MERGE METHODMINUTE MOD MODULE MONTH MULTISET NATIONALNATURAL NEW NIL NO NONE NORMALIZE

NOT NULL NUMERIC OF OFFSET OLDON ONLY OPEN OR ORDER OUT

OVER OVERLAY PARAMETER PARTITION POSITION POWERPRECISION PREPARE PRIMARY PROCEDURE RANGE RANK

REAL RECURSIVE REF REFERENCES REFERENCING RELEASERESULT RETURN REVOKE RIGHT ROLLBACK ROLLUPROW ROWS SCOPE SCROLL SEARCH SECOND

SELECT SET SIMILAR SOME SPECIFIC SQLSTART STATIC SUM SYMMETRIC SYSTEM TABLETHEN TIME TIMESTAMP TO TRANSLATE TREAT

TRIGGER TRUNCATE TRIM TRUE UNION UNIQUEUNKNOWN UPDATE UPPER USER USING VALUEVALUES VARCHAR VARYING VERSION WHEN WHENEVERWHERE WINDOW WITH WITHIN WITHOUT YEAR

IfyouthinkthatanSQLdatabaseisjustacollectionoftables,thenyouarewrong.Thereareadditionalstructuresthatneedtobespecifiedtomaintaintheintegrityofyourdata,suchasschemas,domainsandconstraints.

Schema–Thisisalsocalledtheconceptualvieworthecompletelogical

viewthatdefinestheentiredatabasestructureandprovidesoveralltableorganization.Suchschemaisconsideredametadata–storedintablesandpartofthedatabase(justliketablesthatconsistofregulardata).

Domain–Thisspecifiesthesetofallfinitedatavaluesyoucanstoreinaparticulartablecolumnorattribute.Forexample,inourpreviousCUSTOMERTABLEtheSTATEcolumncanonlycontainthevalues“TX”,“NY”,“CA”and“NV”ifyouonlyprovideproductsandservicesinthestatesofTexas,NewYork,CaliforniaandNevadarespectively.SothesefourstateabbreviationsarethedomainoftheSTATEattribute.

Constraint–Oftenignoredbutoneoftheimportantdatabasecomponents,thissetsdowntherulesthatidentifywhatdatavaluesaspecifictableattributecancontain.Incorporatingtightconstraintsassuresthatdatabaseusersonlyentervaliddataintoaparticularcolumn.Togetherwithdefinedtablecharacteristics,columnconstraintsdetermineitsdomain.UsingthesameSTATEcolumnasanexamplewiththegivenconstraintofonlythefourvalues,ifadatabaseuserenters“NJ”forNewJersey,thentheentrywillnotbeaccepted.ThesystemwillnotproceeduntilavalidvalueisenteredfortheSTATEattribute,unlessthedatabasestructureneedstobeupdatedduetosuddenbusinesschanges.

SQLCommandTypesBeforeyoustartprogramminginSQL,youneedtounderstanditsbasiccommandcategoriesinperformingvariousfunctions–databasecreation,objectmanipulation,datapopulationandupdate,datadeletion,querysubmission,accesscontrolanddatabaseadministration,amongothers.Thefollowingarethemaincategories:

DataDefinitionLanguage(DDL)

DataDefinitionLanguage(orsimplyDDL)enablesyoutocreate,changeorrestructure,andevendestroythebasicelementsthatarecontainedinarelationaldatabase.DDLfocusesonlyonthestructure,notthedatacontainedwithintheelements.Thesebasicelementsordataobjectsincludetables,schemas,viewsandmore.Havingnoindependent

physicalexistence,aviewisregardedasavirtualtableinwhichitsdefinitiononlyexistsinthemetadata.However,theview’sdatacomesfromthetable(ortables)whereyouwillderivetheview.StatedbelowaresomeofthemostcommonDDLcommands:

CREATE–Thiscommandstatementisresponsibleforbuildingthedatabasestructure.Itssyntaxis:

CREATETABLECREATEVIEW

ALTER–Thiscommandstatementisinchargeofchangingthedatabasestructureafterithasbeencreated.Itssyntaxis:

ALTERTABLEALTERVIEW

DROP–ThiscommandisthereverseoftheCREATEstatement,whichdestroysthedatabasestructure.Itssyntaxis:

DROPTABLEDROPVIEW

DataManipulationLanguage(DML)

DataManipulationLanguage(orsimplyDML)consistsofSQLcommandsthathandledatamaintenancefunctions.Thismeansthatyouareabletomanipulatethedatacontainedwithintherelationaldatabaseobjects.Thecommandstatements,whichreadlikenormalEnglishsentences,willallowyoutoenter,change,removeorretrievedata.ThefollowingaretheDMLstatementscommonlyused:

INSERT–Thiscommandstatementisusedtoinsertnewdata

valuesintoacertaintable.Toaddvaluesintoatablewithtwocolumns,usethefollowingsyntax:

INSERTINTOTABLE_NAMEVALUES(‘value1’,‘value2’);TABLE_NAMEisthenameofthetablewhereyouwillbeaddingthenewvalues.ThenumberofitemsinsidetheVALUESparenthesisrepresentsthenumberofcolumnsofthetable,whicharearrangedinthesameorderasthesaidcolumns.Ifthevaluesareofcharacterordate/timedatatypes,theyneedtobeenclosedbysinglequotationmarks.Thisisnotrequiredfornumericornullvalues(thenullvalueshouldbewrittenasNULL).

UPDATE–Thiscommandstatementisusedtomodifyoralterpre-existingdatavaluesinatable,notaddorremoverecords.Theupdateisdoneonetableatatimeormultiplerows/columnsofonetablewithinadatabase.Tochangeasinglecolumn,usethefollowingsyntax:

UPDATETABLE_NAMESETCOLUMN_NAME=‘value’[WHERECONDITION];AslongasthegivenWHEREclauseissatisfied,thenthevalueoftheCOLUMN_NAMEwillbeupdated.ThiscouldbewithinoneormultiplerecordsofthegivenTABLE_NAME.

DELETE–Thiscommandstatementdeletescertainrecordsoreventheentiretable,notdatavaluesfromspecificcolumns.Toremoveasinglerowormultiplerecordsfromatable,usethefollowingsyntax:

DELETEFROMTABLE_NAME[WHERECONDITION];TheWHEREclauseisan

importantpartofthiscommandifyouwanttodeleteselectedrowsfromtheTABLE_NAME.

DataQueryLanguage(DQL)

DataQueryLanguage(orsimplyDQL)consistsofcommandsthatperformdataselection,whichisthemainfocusofrelationaldatabaseusersintheworldofSQL.ThestatementusedisSELECTthatcanbeaccompaniedbyotherclausesoroptionssothatyourextractedresultswillbeinanorganizedandreadableformat.Youcansubmitaquerytothedatabaseusingaseparateapplicationinterfaceorjustasinglecommand-line.ThefollowingisasyntaxforasimpleSELECTstatement:SELECT[*|ALL|DISTINCTCOLUMN1,COLUMN2]

FROMTABLE1[,TABLE2];Usingtheasterisk(*)meansthatallcolumnsofthegiventableareincludedintheoutputandwillbedisplayed.TheALLoptionextractsanddisplaysallvalues,evenduplicates,foracolumn.Ontheotherhand,usingthekeywordDISTINCTpreventsduplicaterowsfrombeingincludedanddisplayedintheoutput.WhatfollowstheFROMkeywordisalistofoneormoretableswhereyouwanttogetthedata.Thecolumnsandtablesspecifiedinthesyntaxareallseparatedbycommas.

DataControlLanguage(DCL)

DataControlLanguage(orsimplyDCL)consistsofcommandsthatallowyoutomanagedataaccesswithinthedatabase.Furthermore,thedatabaseisprotectedfromaccidentalorintentionalmisusebycontrollinguserprivileges.DCLconcentratesontransactions,whichcaptureallSQLstatementsthatperformdatabaseoperationsandsavetheminalogfile.ThefollowingarethecommonDCLcommandstatements:

GRANT–Thisstatementprovidesyouwithcertainprivileges,

likegivingyouthepermissiontoaccessthedatabase.Itssyntaxis:

GRANTPRIVILEGE1,PRIVILEGE2,…TOUSER_NAME

REVOKE–Thisstatementrevokesyourprivileges,likeremovingyourpermissiontoaccessthedatabase.Itssyntaxis:

REVOKEPRIVILEGE1,PRIVILEGE2,…TOUSER_NAME

TransactionalControlCommands

Transactionalcontrolcommandsallowuserstomanipulatevarioustransactionsinmaintainingdatabaseintegrity.InSQL,transactionsbeginwhenapplicationsareexecuted.TheveryfirsttransactionisstartedattheonsetoftheSQLapplication,whilethelasttransactionisendedwhentheapplicationisterminated.Thefollowingarethecommontransactionalcontrolcommands:

COMMIT–Thisstatementcompletesatransactionbymakingthechangesyoumadetothedatabasepermanent,orsimplysavingthetransactions.Itssyntaxis:

COMMIT[WORK];Inthepreviouscommandline,thekeywordWORKisoptional.

ROLLBACK–Thisstatement’sprimaryfunctionistorestorethedatabasesystemtoitspreviousstateorundoalltheactionsthattookplaceinthetransactionlog.Itssyntaxis:

ROLLBACK[WORK];Inthepreviouscommandline,

thekeywordWORKisoptional.

SAVEPOINT–ThisstatementworkswiththeROLLBACKcommand,whereinitcreatessectionsorpointswithingroupsoftransactionsinwhichyouwillbeperformingtheROLLBACKcommand.Itssyntaxis:

SAVEPOINTSAVEPOINT_NAME;SQLiteInstallationInstructionsandDatabaseFeaturesBeforeyoustartoverwhelmingyourselfwithvariousdatabasesolutionsandSQLcommandlines,youneedtodeterminefirstyourpurposewhyyouarecreatingadatabase.Thiswillfurtherdetermineotherdatabasedesignconsiderationssuchassize,complexity,typeofmachinewheretheapplicationwillrun,storagemediumandmore.Whenyoustartthinkingofyourdatabaserequirements,youneedtoknowuptowhatlevelofdetailshouldbeconsideredinyourdesign.Toomuchdetailwillresulttoaverycomplexdesignthatfurtherwastestimeandeffort,andevenyourcomputer’sstoragespace.Toolittlewillleadtoapoorperforming,corruptandworthlessdatabase.Onceyouaredonewiththedesignphase,thenyoucandecidewhichdatabasesoftwareyoucandownloadtostartyourSQLexperience.

Forthesakeofthise-Book’sdiscussion,SQLite,asimplesoftwarelibrary,willbeusedasastarterdatabaseenginetodesign,buildanddeployapplications.Afreeandstand-alonedatabasesoftwarethatisquicktodownloadandeasytoadminister,SQLitewasdevelopedbyRichardHippandhisteamofprogrammers.Itiswasdesignedsothatitcanbeeasilyconfiguredandimplemented,whichdoesnotrequireanyclient-serversetupatall.Thus,SQLiteisconsideredasoneofthemostwidelyuseddatabasesoftwareapplicationsintheworld.

StatedbelowaresomeofthemajorfeaturesofSQLite:

Transactionsareatomic,consistent,isolatedanddurableCompilationissimpleandeasySystemcrashesandpowerfailuresaresupportedFullSQLimplementationwithastand-alonecommand-lineinterfaceclientCodefootprintissignificantlysmallAdaptableandadjustabletolargerprojectsSelf-containedwithnoexternaldependenciesPortableandsupportsotherplatformslikeWindows,Android,iOS,Mac,Solarisandmore

InusingSQLite,youneedtodownloadSQLiteStudioasyourdatabasemanagerandeditor.Withitsintuitiveinterface,thissoftwareisverylightyetfastandpowerful.Youdon’tevenneedtoinstallit,justdownload,unpackandruntheapplication.FollowthesesimplestepsindownloadingSQLiteStudioonaWindows10computer:

1. Gotohttp://sqlitestudio.pl/?act=about.Youshouldgetthefollowingpage:

2. Checktheversionofyourcomputer’soperatingsystemthenclicktheappropriatelinktostartdownloadingthesoftware.

3. Afterdownloadingthesoftware,gotothefolderwheretheapplicationwassaved(usuallytheDownloadsFolderinWindows).ClickontheExtracttabontopthenchoosetheExtractalloption.

4. YouwillgettheExtractCompressed(Zipped)Foldersdialogbox.ChangethedestinationfoldertoC:\SQLthenclicktheExtractbutton.ThiswillbethefolderwhereallyourSQLitefileswillbesaved.

5. Onceallthefileshavebeenextracted,youwillhavetheSQLiteStudiosubfolder.

6. FindtheapplicationprogramnamedSQLiteStudioinsidethesubfolder.Tocreateashortcutonyourdesktop(soyoucanquicklylaunchtheapplication),right-clickthefilename,selectSendtooptionthenchooseDesktop(createshortcut).

7. Whenyoudouble-clicktheSQLiteStudioicononyourdesktop,

8. youshouldgetthefollowingscreen:

TheDatabaseNavigator(leftpane)showsallthelogicalunitsofthedatabasesuchastablesandviews.ThegraypaneattherightistheSQLWorkAreawhereyouwillwriteyourquerystatements.Youwillhaveabetterunderstandingofthisprogram’sgraphicaluserinterfaceinthesucceedingchapters.

InthischapteryouhavelearntthefundamentalfeaturesoftheSQLdatabaselanguage,whichincludesprogramflow,syntaxcharacteristic,reservedwordslist,schema,domain,constraintandmore.ThemaincategoriesofSQLcommandswerealsointroduced,thatgovernthevariousfunctionsoftheprogramminglanguage.YouwerealsogivenaguideonhowtodownloadandinstallSQLiteandSQLiteStudioforyourapplicationsoftware.InthenextchapteryouwilllearnthedefinitionofdataanditsvarioustypessupportedbythedifferentSQLimplementations.

ChapterFour:DataTypes

Inthischapteryouwilllearnwhatdatais,itscharacteristicsandthevarioustypesthattheSQLprogramminglanguagesupports.Therearedifferentgeneraltypesofdatathatarefurthercategorizedintoseveralsubtypes.However,itisadvisablethatyouusedefineddatatypestoensuretheportabilityandcomprehensibilityofyourdatabase.

DefinitionofData

Sincedatabaseisacollectionofinformation,itcanstorenames,numbers,images,calculations,financialamounts,charactersandsoon.Thisstoredinformationiswhatyoucalldata,whichyoucanchangeormanipulateanytimeyouwant.Whenyoustartprovidingrulesonhowyouwriteandstoredata,thenyouaredealingwithdatatypes.Datatypestakeintoconsiderationthelengthallocatedbythedatabaseforeverycolumninthetableandwhatvaluesitcouldcontain-whetheritisalphanumeric,justnumbers,graphics,dateortime.Bydefiningwhatdataisstoredineachdatabasefield,youarepreventingtheoccurrenceofdataentryerrors.Thisformofvalidationthatcontrolsincorrectdatatobeenteredintothedatabaseisalsocalledfielddefinition.

Eachdatabasefieldwillhaveaspecificvalueifitcontainsadataitem.Therearetimes,however,thatacertainfielddoesnothaveanydataitematall.Inthiscase,thefield’svalueisconsiderednull-meaningthevalueisnotknown.Thisnullvalueisdifferentfromthenumericzerovalueortheblankcharactervalue,sincezeroesandblanksaredefinitevalues.Thefollowingarescenarioswhenyoumayhaveanullvalue:

Youdon’tknowwhatthevalueisyetevenifitpossiblyexists.Thevaluedoesnotexistyet.Thevalueisoutofrange.Thefieldisnotapplicableforaparticularrow.

TypesofData

ThefollowingarethegeneraldatatypespredefinedintheSQLlanguage(thatarefurthercategorizedintosubtypes):

Numeric–Thevaluedefinedbythenumericdatatypeissomekindofanumber,whichcouldeitherbeexpressedwithanexactorjustanapproximatevalue.

ExactNumeric

INTEGER–Thisconsistsonlyofwholenumbersthatarebothpositiveandnegative.Itdoesnotcontainadecimalnorafractionalpart.Thevaluerangesfrom-2,147,483,648to2,147,483,647,withanallocated4bytesofstoragesize.

SMALLINT–Thisisusedinreplacementofintegerstosavestoragespace,butwithaprecisionthatcannotbelargerthanthatofaninteger.Precisionincomputerprogrammingisthemaximumtotalofsignificantdigitsanumbercanhave.Thevaluerangesfrom-32,768to+32,767,withanallocated2bytesofstoragesize.

BIGINT–ThisisthereverseoftheSMALLINT,whereitsminimumprecisionisthesameastheINTEGERdatatypeorgreater.Thevaluerangesfrom-9,223,372,036,854,775,808to9,223,372,036,854,775,807,withanallocated8bytesofstoragesize.

NUMERIC(p,s)–Inadditiontotheintegerpart,thisdatatypealsocontainsafractionalcomponentthatindicatestheprecisionandscaleofthevalue.Scaleisthenumberofdigitsorplacesreservedinafractionalpartofthedata,locatedattherightsideofthedecimalpoint.InNUMERIC(p,s),‘p’specifiestheprecisionwhile‘s’isforthescale.Forexample,NUMERIC(6,3)meansthatthenumber’sabsolutevaluewillonlybeupto999.999(6totalsignificantdigitswith3digitsfollowingthedecimalpoint).

DECIMAL(p,s)–LiketheNUMERICdatatype,thishasafractionalcomponentwhereyoucanspecifyboththevalueprecisionandscale.However,thisdatatypeallowsgreaterprecision.Forexample,DECIMAL(6,3)cancontainvaluesupto999.999butthedatabasewillstillacceptvalueslargerthan999.999.Letussayyouenteredthenumber123.4564,thiswillberoundedoffto123.456.Theallocatedstoragesizeforthisdatatypeisbasedonthegivenprecision.

ApproximateNumeric

REAL(s)–Thisconsistsofasingle-precision,floating-pointnumberwherethedecimalpointcan“float”todifferentplacesinthesaidnumber.Thismeansthatthisdatatype’sdecimalvaluehasalimitlessprecisionandascaleofvariablelengths.Forexample,thevaluesforπ(pi)caninclude3.14159,3.14and3.1(eachvaluehasitsownprecision).Forsingle-precision,floatingpointnumbers,theirprecisionisbetween1and21inclusive.Italsoallocates4bytesofstoragesizeforitsvalues.

DOUBLEPRECISION(p,s)–Thisconsistsofa

double-precision,floating-pointnumberandthecapacityistwiceoftheREALdatatype.Thisdatatypecomesinhandywhenyourequiremoreprecisenumbers,likeinmostscientificfieldofdisciplines.Fordouble-precision,floatingpointnumbers,theirprecisionisbetween22and53inclusive.Italsoallocates8bytesofstoragesizeforitsvalues.

FLOAT(p,s)–Thisisthedatatypethatallowsyoutospecifytheprecisionandletsthecomputerdecidewhetheryouwillgoforasingle-oradouble-precision.ItactuallypertainstobothREALandDOUBLEPRECISION,dependingontheprecisionyouhavespecified.Becauseofthischaracteristic,itiseasiertomovethedatabasefromonecomputerplatformtoanother.

String–Thestringdatatypestoresalphanumericinformationandisalsoconsideredasoneofthemostcommonlyuseddatatypes.

CHARACTER(n)orCHAR(n)–Thisdatatypeisalsoknownasafixed-lengthstringoraconstantcharacter.Thismeansthatallthestringsstoredinthatparticularcolumnhavethesamelength,whichisrepresentedby‘n’(thenumberofcharactersorthemaximumallocatedlengthforthedefinedfield).Forexample,ifyousetthecolumn’sdatatypetoCHAR(23)thenthemaximumlengthofanydataenteredinthefieldis23characters.Ifthestring’slengthislessthan23,thenSQLfillstheremainingspaceswithblanks.Thisisthedrawbackofusingfixed-lengthstringsbecausestoragespaceiswasted.Ontheotherhand,ifthereisnovalueprovidedfor‘n’,thenSQLassumesalengthofonecharacter.ThemaximumlengthfortheCHARACTERdatatypeis254.

CHARACTERVARYING(n)orVARCHAR(n)–Thisisusedwhenthedataentriesareofdifferentlengths,ornotconstant,butyoudon’twantSQLtofilltheremainingspaceswithblanks.Thus,theexactnumberofcharactersyouenterwillbestoredinthedatabase-furthersavingstoragespace.Thisdatatypehasnodefaultvalueanditsmaximumlengthis32,672characters.

CHARACTERLARGEOBJECT(CLOB)–IntroducedinSQL:1999,thisvariable-lengthdatatypeisusedtocontainunicodecharacter-basedinformationthatistoobigtobestoredasaCHARACTERtype,suchaslargedocuments.ThemaximumvalueofaCLOBisupto2,147,483,647characterslong.

DateandTime–Thisdatatypemanagesanyinformationconcerningdatesandtimes.

DATE–Thisdatatypeprovidesstoragefortheyear,monthanddayvaluesofadate,inthatparticularorder.Theyearvalueisexpressedusingfourdigits,whichcanberepresentedbyanyvaluerangingfrom0001upto9999.Asforthemonthanddayvalues,theyarebothexpressedusingtwodigits.Theformatforthedatedatatypeisyyyy-mm-dd.

TIME–Thisdatatypestoresanddisplaystimevalueswithanhour-minute-secondformat(“HH:MM:SS”).

DATETIME–WhenthevaluecontainsbothdateandtimeinformationthenyouusetheDATETIMEdatatype,whichisdisplayedusingthe“YYYY-MM-DDHH:MM:SS”format.Thevalidrangeofvaluesforthistypeisfrom“1000-01-0100:00:00”to“9999-12-3123:59:59”.

TIMESTAMP–ThisissimilartotheDATETIMEdatatypebuttherangeofvaluesisfrom“1970-01-0100:00:01”UTCto“2038-01-1903:14:07”UTC.

Boolean–Thisdatatypeconsistsofvaluesthatareusedfordatacomparison:TRUE,FALSE,orNULL.Fordatatobereturned,alltheconditionsofthespecifiedcriteriaforagivenqueryshouldbemet–meaningtheBooleanvalueisTRUE.Ifdataisnotreturned,thenthevalueiseitherFALSEorNULL.

User-DefinedDataType

Afterlearningthegeneralpredefineddatatypes,youwillnowmovetouser-defineddatatypesorsimplyUDTs.Bythenameitself,thesearethedatavaluesthattheuserdefinesorspecifiesbasedontheexistingdatatypes.Thus,customizationisallowedtomaximizestoragespaceandmeetotheruserrequirements.Furthermore,databaseapplicationdevelopmentbecomesmoreflexibleforprogrammers.ThismeansthatyoucanuseUDTswhenyouneedtoenterthesametypeofdatainacolumnthatwillbedefinedinseveraltables.TodefineUDTs,youcanusetheCREATETYPEstatement.

Forexample,ifyouwanttodefineanddifferentiateUSDollarandUKPoundastwocurrenciesforyourdatabasethencreatethefollowingUDTS:

CREATETYPEUSDollarASDECIMAL(9,2);

CREATETYPEUKPoundASDECIMAL(9,2);

EvenifbothdatatypeswerecreatedusingthepredefinedDECIMALtype,eachhasitsownfunctionandcharacteristicinthedatabase.Goingbacktothesamplecustomerandorderinformationfromthepreviouschapters,youcannowcreatethefollowinginvoicetablesthatincludethetwoUDTs:

CREATETABLEAmericaInvoice(InvoiceIDINTEGERPRIMARY

KEY,CustomerIDINTEGER,OrderIDINTEGER,TotalSaleAmtUSDollar,ShippingFeeUSDollar

CREATETABLEUnitedKingdomInvoice(InvoiceIDINTEGERPRIMARY

KEY,CustomerIDINTEGER,OrderIDINTEGER,TotalSaleAmtUSDollar,ShippingFeeUSDollar

InthischapteryouhavelearntthecharacteristicsofthevariousdatatypesavailableintheSQLlanguage.Youwerealsoabletounderstandtheneedtocreateuser-defineddatatypestomakeyourdatabaselesscomplicatedandmoreportable.InthenextchapteryouwilllearnhowtousethedifferentDataDefinitionLanguagestatementsincreatingdatabaseobjectsusingSQLiteStudio.

ChapterFive:DataDefinitionLanguageStatements

InthischapteryouwillgainadeeperunderstandingofthethreeDataDefinitionLanguagestatements–CREATE,ALTERandDROP.UsingSQLiteStudio,youwillalsolearnhowtoencodethecorrespondingSQLstatementsthathandlethedatabasestructure.

Again,adatabaseobjectisanydefinedlogicalunitthatstoresorreferencesdata.Whenyouhaveacollectionofdatabaseobjects,youcreateaschemathatisassociatedwithoneparticulardatabaseowner.Thefocusofthischapteristhebasicformofdatastorage,whichistherelationaldatabasetable.Asimpletablefurtherconsistsofrows,whichcorrespondstotherecordsofdata,andcolumns,whicharealsoknownasfieldsthatcontainanassignedparticulartypeofdata.Adatabasetablewillalwayshaveatleastonecolumnandarowthatiscomposedofoneormorefields.

CREATEStatementThenumerousformsoftheSQLCREATEstatementareresponsibleforconstructingvitaldatabasestructuresandobjects–tables,views,schemas,domainsandsoon.Theactofcreatingtablescouldbeeasy,butyouneedtotakeintoconsiderationnumerousfactors.Planningtablestructuresbeforeactualimplementationcouldsaveyoutimeandeffortsinceyoudonotneedtoreconfigureafterthetableshavebeencreated.

Herearesomeofthefactorstotakeintoconsiderationthroughwhencreatingtables:

TypeofdatathetablewillcontainTableandcolumnnamesPrimarykey(thecolumnthatmakeseachrowofdatauniquetoavoidduplicaterecordsinatable)ColumnlengthColumnscontainingnullvalues

Syntax:CREATETABLETABLE_NAME(field1DATA_TYPE[notnull],field2

DATA_TYPE[notnull],field3DATA_TYPE[notnull],field4DATA_TYPE[notnull],field5DATA_TYPE[notnull]);Thecolumnnames(field1,field2,field3,field4andfield5)andthefielddatatypesarewritteninsidetheparenthesis,separatedbycommas.Anythingindicatedinsidethebracketsareconsideredoptionalandthesyntaxstatementfinallyendswithasemicolon.

UsingtheCUSTOMERTABLEfromChapter2,youwillcreateanewdatabasetableusingSQLiteStudio.

CreateaNewDatabase

1. OpenSQLiteStudiobydouble-clickingtheapplicationicononyourdesktop.

2. ClicktheDATABASEmenuthenselectADDADATABASE.

3. TypeSample_DBinsidetheFILEinputbox(whichisthenameofthenewdatabase)thenclickOK.

4. YouwillnowhavetheSample_DBobjectinsidetheDatabase

Navigatorpane.

CreateaNewTable

1. ClicktheTOOLSmenuthenselectOPENSQLEDITOR.YouwillhavetheSQLeditorareaattherightpane.Ifyoudouble-clickSample_DB,youwillseeTABLESandVIEWSunderthedatabaseobject.Rightnow,therearenotablesnorviewspresentsoyouwillcreateoneusingtheSQLEditorpane.

2. UndertheQUERYTab,typethefollowinglinesofcode

CREATETABLECustomer_TBL(CustomerIDINTEGERNOTNULLPRIMARYKEY,

CustomerNameVARCHARNOTNULL,JobPositionVARCHAR,CompanyNameVARCHARNOTNULL,USStateVARCHARNOTNULL,ContactNoBIGINTEGERNOTNULL);

3. ClicktheEXECUTEQUERYbutton ontopoftheQUERYTaborpressF9onthekeyboard.YouwillnowhavetheCustomer_TBLtablewith6columns.

ALTERStatementTheSQLALTERstatementisusedtomodifydatabaseobjects,specificallytables.Alteringtableelementscanincludeaddinganddroppingcolumns,changingcolumndefinitions,addinganddroppingconstraints,modifyingtablestoragevaluesandmore.

Syntax:ALTERTABLETABLE_NAME[modify][columnCOLUMN_NAME]

[DATATYPE|nullnotnull][restrict|cascade][drop][constraintCONSTRAINT_NAME][add][column]COLUMNDEFINITION;AlteraTablebyAddingaNewColumn

1. AnewcolumnthatcontainsthecompanyaddressofthecustomerwillbeaddedtotheCustomer_TBLtable.TypethefollowinglinesofcodeundertheQUERYtab:ALTERTABLECustomer_TBLADD

CompanyAddVARCHAR;

2. AfterclickingtheEXECUTEQUERYbutton ,theCompanyAddcolumnisaddedaftertheContactNocolumn.Thisfieldcontainsvaluesofstringdatatype.

DROPStatementYouusetheSQLDROPstatementifyouwanttodelete

databaseobjects.Thus,theDROPTABLEstatementisusedtodeletetablesthatyoudonotneedanymore.Oncethislineisexecuted,allthedataandmetadatacontainedinthetablearealsoremoved.DROPTABLEisconsideredtobetheeasiestcommandtoexecute.However,anerrorwilloccurifthetabletobedeletedisbeingreferencedbyanothertableinthedatabase.ThatiswhyyouneedtobecautiouswhenperformingtheDROPstatementtoavoiddeletingobjectsbymistake(mostespeciallyiftherearemultipleuserswhoaccessthedatabase).

Syntax:DROPTABLETABLE_NAME[restrict|cascade]

TheRESTRICToptionisusedifanerroristobereturnedwhenatablereferencedbyanotherdatabaseobjectisdropped.Ontheotherhand,theCASCADEoptionallowsthetableandallotherreferencingobjectstobedeleted.TherearesomeSQLapplicationprogramsthatdonotpermittheCASCADEoptiontoguaranteethattherewillbenoinvaliddatabaseobjects.

DropanExistingTable

1. Sincethereisonlyonetableinthedatabase(Customer_TBL),youdonotneedtoworrywhethertousetheRESTRICTortheCASCADEoption.SimplyenterthefollowinglineofcodeinsidetheQUERYtab.

DROPTABLECustomer_TBL;

2. ClicktheEXECUTEQUERYbutton andinstantlytheCustomer_TBLtableisdeleted.

InthischapteryouhavelearnthowtoencodeprogramminglinesusingthecommonDDLcommandstatementsincreating,alteringanddroppingdatabasetablesinSQL.InthenextchapteryouwilllearnthedifferentDMLcommandsthatwillallowyoutomanipulateinformationcontainedindatabasetables.

ChapterSix:DataManipulationLanguageStatements

Inthischapteryouwilllearnhowtomanipulatedatabasetablesandmakethemusefulthroughdatainsertion,deletionandupdate.Toaccomplishthis,youwillbeprogramminginSQLiteStudiousingthreeDataManipulationLanguagestatements–INSERT,DELETEandDROP.

Normally,suchtablesareemptyaftertheyhavebeencreated.Thedatathatyoucanstoreinyourdatabaseobjectscanbeinvariousformats–non-digital,semi-digitalandfullydigital.Non-digitalformatmeansthatthedataneedstobeextractedfromanon-electronicsource,likecustomerinformationfrombusinesscards.Inthiscase,youarerequiredtostorethedatamanuallyintoyourdatabase.Asforthesemi-digital,thedatacouldalreadybeinsomesortofdigitalformbutnotthesameformatasyourdatabasetables.Forexample,youcouldhaverecordsofyourcustomers’businesscardsstoredinaMicrosoftExcelfilethatyoumayneedtotranslateintoanappropriateformatfitforyourdatabase.Lastly,fullydigitalmeansthatallofyourcustomerinformationisalreadyinelectronicformatthatalsomatchesthelayoutofyourdatabase.

Thecurrentdataformatwillfurtherdeterminehowyouwillbeabletomanipulateyourdatabase.ThisiswheretheDMLcommandsbecomeusefulinenteringnewdata,updatingexistingdataanddeletingdatafromtables.

INSERTStatement

Theprocessofenteringnewdatacouldbedoneeithermanuallythroughindividualcommandsorautomaticallyusingbatchprocessprograms.Therearealsofactorsthatwilldeterminewhatandhowmuchdatayoucaninsertinyourdatabasetables–fieldlength,columndatatype,tablesizeandmore.Inpopulatingtableswithdata,youwillusetheINSERTstatement.

OneRowataTime

Whenyouwanttoenterallthedataintoasinglerowofyourdatabasetable,youcancreateaform-baseddataentryapplication.Inthisfeature,ascreenisdesignedthatcontainsfieldswhereyoucaninputtheinformationbeingasked-foreverycolumninthetable.Usethefollowingsyntaxinaddingdataonerowatatime:

INSERTINTOTABLE_NAME[(column_1,column_2,…,

column_n)]VALUES(value_1,value_2,…,value_n);

Anythinginsidethesquarebracketsareconsideredoptional,meaningyoudon’tneedtolistthecolumnnames.Bytheway,“n”isthemaximumnumberoftablecolumns.Thedefaultorderofthecolumnlististhesameorderasyourcolumntables.Thus,ifyoulisttheitemsinsidetheVALUESsectioninthesameorderasyourtablecolumns,thenthevalueswillbeenteredinthecorrectcolumns.Youonlyneedtoindicatethecolumnnamesifyouneedtospecifythevaluesinadifferentorder.

Now,letusinsertrecordstoourCustomer_TBLtableusingthecustomerinformationprovidedintheChapter2.

1. TypethefollowingprogramminglinesintheSQLeditor:

INSERTINTOCustomer_TBL(CustomerID,CustomerName,

JobPosition,CompanyName,USState,ContactNo)

VALUES(1,‘KathyAle’,‘President’,‘TileIndustrial’,‘TX’,3461234567)

2. ClicktheEXECUTEQUERYbutton andyouwillgetthefollowingscreen(thereshouldbenoerrorsintheStatusArea):

3. Tocheckiftherecordofdatawasinsertedinthetable,double-clickCustomer_TBLattheleftpane.ClicktheDATAtabattherightpane,whichisinbetweenSTRUCTUREandCONSTRAINTStabs.Yourtableshouldbesimilartowhatisshowninthescreenbelow:

4. Clickthe optionatthebottomleftcornerofthescreen.Toaddanotherrecordwithoutspecifyingthecolumnnames,deletetheprogrammingcodesinsidetheQUERYtabandtypethefollowinglines:

INSERTINTOCustomer_TBLVALUES(2,‘KevinLord’,‘VP’,‘BestTooling’,‘NY’,5181234567)

5. ClicktheEXECUTEQUERYbutton andprovidedthattheorderofthevaluescorrespondsexactlytotheorderoftheCustomer_TBLtable’scolumns,thenthereshouldbenoerrorsintheStatusArea.

6. ClicktheCUSTOMER_TBL(SAMPLE_DB)option

atthebottomleftcornerofthescreen.UndertheGRIDVIEWtab,click

theREFRESHTABLEDATAbutton orpressF5onyourkeyboard.Youshouldseethenewrecordaddedtothetable.

MultipleRowsataTime

Multipleinsertsarebeneficialifyouneedtoenteranumberofrecordsintoyourtable.Thisprocessisalsomoreefficientratherthaninsertingonerecordatatime.AllyouneedtodoisrepeattheclausefollowingtheVALUESstatementandmakesureyouseparatethemwithacomma.

ToinsertthetworemainingrecordsintoourCustomer_TBL(seeChapter2forthedetails):

1. GoingbacktotheSQLEditor,enterthefollowinglinesofcodes(withoutspecifyingthecolumnnamesanymore):

INSERTINTOCustomer_TBLVALUES(3,‘KimAsh’,‘Director’,‘CarWorld’,‘CA’,5101234567),(4,‘AbbyKarr’,‘Manager’,‘WestMart’,‘NV’,7751234567)

2. ClicktheEXECUTEQUERYbutton .

3. Gotothe

option.Makesuretoclickthe

REFRESHTABLEDATAbutton orpressF5onyourkeyboard.Youshouldnowseetwomorerecordsinsertedtothedatabasetable.

OnlySelectedColumnsataTime

InChapter5,theJobPositionfieldofCustomer_TBLtablewasdefinedtoallownullvalues.Ifincaseyouhaveanewcustomerbutyoudonotknowhispositionyetinthecompany,thenyoucanleavetheJobPositionfieldblankwhileprovidingthenecessaryinformationfortherestofthefields.

ToaddanewrecordwithoutprovidingdatafortheJobPositionfield:

1. EnterthefollowingSQLlines(makesureyouindicatethecolumnnames):

INSERTINTOCustomer_TBL(CustomerID,CustomerName,CompanyName,USState,ContactNo)VALUES(5,‘MikeArmhs’,‘1DrivingSchool’,‘NJ’,2011234567)

2. ClicktheEXECUTEQUERYbutton ontopoftheQUERYtab.

3. Gotothe optionthenclicktheREFRESH

TABLEDATAbutton orpressF5onyourkeyboard.NoticethatsinceyoudidnotprovideanyinformationfortheJobPosition

field,itcontainsaNULLvalue.

UPDATEStatement

Sincechangeisinevitable,SQLprovidesawayforyoutoupdateexistingdatastoredinyourdatabase.Dependingonyourneeds,youcanmodifyasinglerecordormultiplerecordsatonetimeusingtheUPDATEcommand.However,onlyonetableisgenerallyupdatedatatimeinagivendatabase.ThestandardsyntaxforthisDMLstatementis:

UPDATETABLE_NAMESETcolumn_1=EXPRESSION_1,column_2=EXPRESSION_2,…

column_n=EXPRESSION_N[WHEREpredicates];

Again,anythinginsidethebracketsthatisindicatedintheWHEREclausestatementisoptionalandthemaximumnumberofcolumnsisrepresentedby“n”.Thesaidclauseidentifieswhichrowsneedtobeupdated-thismeansthatiftheWHEREclauseisnotpresentthenalltherecordsofthetableareautomaticallymodified.

OneRecordataTime

Fromthepreviousdiscussion,youaddedarecordofcustomerinformationwithoutprovidingdatafortheJobPositionfield.Ifincaseyouhavelearnedthatthecontactpersonisthevice-presidentofthecompany,thenyoucanmodifythisexistingrecord.

1. GobacktotheSQLEDITORbyclickingtheoption.Enterthefollowinglinesofcode:UPDATECustomer_TBL

SETJobPosition=‘VP’WHERECustomerName=‘MikeArmhs’;

3. Clickthe optionthenclickthe

REFRESHTABLEDATAbutton orpressF5onyourkeyboard.Youwillnowsee‘VP’undertheJobPositionfieldforthecustomernamedMikeArmhs.

MultipleRecordsataTime

Now,ifyouwanttomodifythe‘VP’valueoftheJobPositionfieldto‘Vice-President’soitwillbemorecomprehensibletodatabaseusers,thenyouhavetoupdatemultiplerecordsatonetime.

1. Clickthe optionatthebottomleftcornerofthescreenandthenchangetheprogramminglinesintothefollowing:

UPDATECustomer_TBL

SETJobPosition=‘Vice-President’WHEREJobPosition=‘VP’;

REFRESHTABLEDATAbutton orpressF5onyourkeyboard.Youshouldnowseethattheprevious‘VP’valuehasbeenchangedto‘Vice-President’.

AllRecordsataTime

Ifyouwanttogivemoreemphasistothecustomernamebychangingittouppercaseletters,thenyoucanmodifyalltherecordsofthedatabasetableatonetime.Inthiscase,youwillnotbeneedingtheWHEREclauseanymore.

1. Clickthe optionatthebottomleftcornerofthescreenandthenenterthefollowingprogramminglines:

UPDATECustomer_TBL

SETCustomerName=UPPER(CustomerName)

REFRESHTABLEDATAbutton orpressF5onyourkeyboard.Noticethattheformatofthecustomernameforalltherecordsinthetablehavebeenchangedtocapitalletters.

DELETEStatement

TheDELETEstatementisaDMLcommandthatwillremoverecordsfromatablebutwillstillkeepitsexistenceinthedatabase.Thishappenswhenyoudon’tneedaparticularinformationinyourdatabase,eitherbecausetheyareobsoleteorhavenouseanymore.Thus,youcanfreeupsomestoragespace.YoucanexecutetheDELETEcommandtoremovejustonerecord,multiplerecordsorevenalltherecordsofthetableatonetime.Justareminder,thiscommanddoesnotdeletevaluesfromaspecificcolumn,butremovesanentireroworafullrecord.Thatiswhyyouhavetobeverycarefulwhenexecutingthiscommand.ThereisapossibilitythattheeffectoftheDELETEcommandispermanentandyoumaynotbeabletorecovertheeraseddata.ThestandardsyntaxforthisDMLstatementis:

DELETEFROMTABLE_NAME[WHERECONDITION];

EveniftheWHEREclauseisanoptionalpart,youarerequiredtoincludeitwhenyouwanttodeleteselectedrowsofdatafromacertaintable.WithouttheWHEREclause,youwillberemovingalltherecordsfromthetable.

TodemonstratethefunctionoftheDELETEstatement,youwillcreateacopyoftheCustomer_TBLtablefirst.Inthisway,youwillstillbeablekeeptheoriginaltabletobeusedforfurtherexercises.

1. GototheDATABASENAVIGATORthenright-clickonCustomer_TBL.ChooseCREATEASIMILARTABLE.

2. Youwillbeaskedtoprovideanameforyourtable.TypeCustomer_TBL2insidetheTABLENAMEinputbox.

3.Clickonthe

COMMITSTRUCTURECHANGESbutton undertheSTRUCTUREtab.Youwillgetthescreenbelow.

4. ClickontheOKbuttonandanewCustomer_TBL2tablewillbecreated.ThiswillbethetablethatyouwillworkaroundtodemonstratetheDELETEcommand.

AtthispointintimeCustomer_TBL2tableisempty,soyouhavetocopytherecordsfromCustomer_TBLtable.Todothis,followthestepsbelow:

REFRESHTABLEDATAbutton orpressF5onyourkeyboard.Thiswillensurethatyourdatainthedatabasetableisupdated.

2. Clickontopofthefirstrow,justbeforetheCustomerIDcolumnheading.Thiswillhighlightalltherecordsinthetable.

3. Tocopythevalues,right-clickonthefirsthighlightedcell(justundertheCustomerIDcolumn)thenchooseCOPY.

4. Double-clickonCustomer_TBL2locatedintheleftpane.ClicktheDATAtabandmakesurethatyouareontheGRIDVIEWtab.Youwillseethesamecolumnsasintheoriginaltable,whichyouwillbepopulatingwiththedatayoucopiedfromtheCustomer_TBLtable.

5. ClickthedropdownarrowbesidetheINSERTROWbutton(justbelowtheGRIDVIEWtab).SelectINSERTMULTIPLEROWSoption.

6. InsidetheNUMBEROFROWSTOINSERTinputboxtype5.ClickOK.

7. Yourtablewillnowhave5rowsofdatathatcontainNULLvalues.ThisiswhereyouwillinsertthevaluesthatyoucopiedfromtheCustomer_TBLtable.

8. Right-clickonthefirstcellthenchoosethePASTEoption.

9. AllthedatavaluesfromtheCustomer_TBLtablewillbeinsertedtotheCustomer_TBL2table,whichyouwillmanipulatetodemonstratetheDELETEcommand.

10.ClickontheCOMMITSTRUCTURECHANGESbutton

tosavethedatainthetable.

SingleRecord

TodeleteonlyonerecordofdatafromtheCustomer_TBL2tablewherethecustomer’snamematchesto‘KATHYALE’:

1. Clickthe option,typethefollowinglinesofcodeintheQUERYtabandthenclicktheEXECUTEQUERYbutton

DELETEFROMCustomer_TBL2

WHERECustomerName=‘KATHYALE’;

2. Tocheckiftherecordhasbeendeleted,gototheCustomer_TBL2tablebyclickingon

.Thenclickonthe

REFRESHTABLEDATAbutton orpressF5onyourkeyboardtoupdatethevalues.Youwillnoticethattherecordhasbeendeletedalready.

MultipleRecords

Todelete2recordsofdatafromtheCustomer_TBL2tablewherethecustomer’spositionmatchesto‘Vice-President’:

1. Clickthe option,typethefollowinglinesof

codeandthenclicktheEXECUTEQUERYbutton .

WHEREJobPosition=‘Vice-President’;

2. Tocheckiftherecordhasbeendeleted,gotothe

Customer_TBL2tablebyclickingon

.Thenclickonthe

REFRESHTABLEDATAbutton orpressF5onyourkeyboardtoupdatethevalues.Youwillnoticethatthetworecordshavebeendeletedalready.

WholeTable

TodeletealltheremainingrecordsfromtheCustomer_TBL2tableatonetime:

1. Clickthe option,typethefollowinglinesofcodeintheQUERYtabandthenclicktheEXECUTEQUERY

button .

2. Tocheckiftherecordhasbeendeleted,gotothe

Customer_TBL2tablebyclickingon

.ThenclickontheREFRESH

TABLEDATAbutton orpressF5onyourkeyboardtoupdatethevalues.YouwillnoticethatexecutingthesingleDELETEcommandhasdeletedalltherecordsfromthetable.

InthischapteryouhavelearnthowtoencodeprogramminglinesusingthemostcommonlyusedDMLcommandstatementsininserting,updatinganddeletingrecordsfromdatabasetablesinSQL.InthenextchapteryouwilllearnthedifferentDQLcommandsthatwillallowyoutoretrievevaluableinformationcontainedindatabasetables.

ChapterSeven:DataQueryLanguageStatements

InthischapteryouwilllearnhowtousetheavailableDataQueryLanguagestatementsinretrievingdatafromdatabasetables.ThroughSQLiteStudio,youwillbeabletouseSELECT,WHERE,ORDERBYandGROUPBYstatementsinrequestinganddisplayingsignificantdatabaseinformation.

Onceyouhavecreatedandpopulatedyourtableswithdatavalues,therewillcomeatimethatyouwillneedtoperformdatabasequeriestoretrieverelevantinformation.Aqueryisavalidinquiryintothedatabasetoextractanddisplaydatainareadableorunderstandableformat,dependingontheuser’srequest.ThemainchallengeinSQListocorrectlyinstructthecomputerwhattosearchforbymanipulatingthedatabasethroughrowselection.Onceyouhaveselectedthevaluesyouneedthenyoucanfurtherperformvariousoperationssuchasdataaddition,deletion,modificationandmore.

SELECTStatement

Retrievingdatavaluesisthemostperformedmanipulationtaskbydatabaseusers.IndoingsuchoperationyouneedtousetheDMLcommandstatementcalledSELECT.Youhavetheoptiontoretrievejustonerow,anumberofrowsoralltherowsofthedatabasetable.

UsingtheSELECTstatementinretrievingalltherecordsofaparticulartableisthebasicformofthisDMLcommandstatement.EveniftheSELECTcommandisconsideredtobethemostpowerfulstatement,itrequiresotherclausestofunctioncorrectlyinperformingaquery.Thesyntaxinitssimplestformis:SELECT*FROMTABLE_NAME;Intheprogramminglineabove,theasterisksign(*)signifieseverything.Thismeansthatthewildcardcharacterisashortcutforthelistingofallthecolumnnamesofaparticulartable.

ToselectallthedatarowsfromtheCustomer_TBLtable:

1. Clickthe optionandthentypethefollowinglinesofcode:

SELECT*FROMCustomer_TBL;

2. ClicktheEXECUTEQUERYbutton .TheresultofthisSELECTcommandisdisplayedinsidetheGRIDVIEWtab.

TheresultbasicallyshowstheentiredataoftheCustomer_TBLtablesincethecodeinstructsthedatabasetoselectalltherowsandcolumnsofthesaidtable.

WHEREStatement

Whenyouwanttobemorespecificinselectingrowsofdatafromyourdatabasetablesthenyouneedtoaddabitofcomplexitytoyourprogramminglines.Atthispoint,youneedthefunctionoftheWHEREclause,whichmeansthattheSELECToperationwillbeperformedoncethestatedconditioninsidesuchclauseistrue.ThesyntaxoftheSELECTstatementwiththeWHEREclauseisasfollows:SELECTCOLUMN_LIST

FROMTABLE_NAMEWHERECONDITION;

ToselectonlytherowsofdatawherethejobpositionofthecustomerisVice-President:

SELECT*FROMCustomer_TBLWHEREJobPosition=‘Vice-President’;

TheresultshowstherecordsofthetwocustomersnamedKevinLordandMikeArmhswhoarebothVice-Presidentsoftheirrespectivecompanies.

Whatifyouonlywanttoselectcertaincolumnsofthetable,maybejustthefullnameandcompanyofthecustomer?Youwillnowmodifyyourlinesofcodeintothefollowing:

1. IntheQUERYtab,changethewildcardcharacter*(asterisksign)intoCustomerNameandCompanyNamebytypingthefollowing:

SELECTCustomerName,CompanyNameFROMCustomer_TBLWHEREJobPosition=‘Vice-President’;

Byspecifyingthecolumnsyouwanttoselect,youaretryingtocustomizewhatdatayouwanttoretrieveandhowyouwantthemtobedisplayed.Inthepreviousexample,youonlywantedtoknowthecustomer’snameandhiscompanywherethejobpositionisvice-president.

ORDERBYandGROUPBYStatements

Whenyouwantthedatayouretrievetobedisplayedandsortedinsomeway,thenyouneedtoincludetheORDERBYorGROUPBYoperatorattheendofyourSQLstatement.TheprimaryfunctionoftheORDERBYstatementisbasicallytoarrangedatausingaspecificorder,whetherascendingordescending.Ontheotherhand,theGROUPBYstatementisusedtoputidenticaldatatogetherandarrangethequeryoutputintogroups.

ThestandardsyntaxfortheORDERBYclauseis:SELECTCOLUMN_LIST

FROMTABLE_NAMEORDERBYCOLUMN_LIST[ASC|DESC];Bydefault,ORDER

BYsortsindividualrowsinascendingorder.IfyouwanttoarrangeyourrecordsindescendingorderthenyouhavetoindicatetheDESCoperatorattheendoftheORDERBYclause.

ToretrieveallcustomerrecordsfromtheCustomer_TBLtableanddisplaytheminascendingorderbyUSstate:

SELECT*FROMCustomer_TBLORDERBYUSState;

Sinceyoudidnotspecifyhowtherecordswillbesorted,thedatarowswerearrangedalphabetically(inanascendingorder)usingtheUSStatecolumn.Ifyouwanttosortyourrecordsindescendingorder:

1. InsidetheQUERYtab,addDESCafterUSStateintheORDERBYclause.

SELECT*FROMCustomer_TBLORDERBYUSStateDESC;

Ifyouwanttodeterminesomethingaboutagroupofrecordsorneedtocombinecolumnswithduplicatevaluesinalogicalway,thenitistimetousetheGROUPBYclause.Othertermssimilartogroupingareaggregating,summarizingandrollingup.Toillustratethis,ifyouwanttoknowhowmanycustomersarethereforeveryjobpositionintheCustomer_TBLtablethenweneedtocountthenumberofrecordsanddisplaythetotalnumberofcustomersperjobposition.

SELECTJobPosition,COUNT(*)ASnumber_of_recordFROMCustomer_TBL

GROUPBYJobPosition;

Intheexampleabove,theCOUNTfunctionwasintroducedtoarrangethedataingroups.ThefollowingisasummaryofthecommonaggregatefunctionsusedtogetherwiththeGROUPBYstatement(xdenotesthecolumnnamewhereyouwanttoperformthefunction):

AVG(x)–computestheaverageofallthecolumnvalues(nullvaluesremoved)COUNT(x)–countsthenumberofnon-nullvaluesinthecolumn

COUNT(*)–countsthenumberofrecords

MAX(x)–computesthemaximumvalueinthecolumn(nullvaluesremoved)

MIN(x)-computestheminimumvalueinthecolumn(nullvaluesremoved)

SUM(x)–computesthesumortotalofthevaluesinthecolumn(nullvaluesignored)

GoingbacktotheGROUPBYexample,thedataintheJobPositioncolumnisretrievedandforeachinstanceofthevalue,arecordiscountedusingtheCOUNTfunction.Thenumber_ofrecordisanewcolumncreatedthatdisplaysthetotalnumberofrecordsperjobposition.TheDirector,ManagerandPresidentpositionshave1recordeachwhiletheVice-Presidenthas2.Thisisbecausetherearetwocustomerswhoarevice-presidents–KevinLordandMikeArmhs.Ifyoucanalsonotice,therecordsdisplayedaresortedinanascendingorderbydefault.

AlteringyourSQLstatementstodisplaythejobpositioninadescendingorderwillrequireyoutoaddtheORDERBYstatementaftertheGROUPBYclause(ORDERBYwillalwayscomeaftertheGROUPBYstatement).ChangeyourlinesofcodeintothefollowingandthenclicktheEXECUTEQUERY

button ontopoftheQUERYtab:SELECTJobPosition,COUNT(*)ASnumber_of_recordFROMCustomer_TBL

GROUPBYJobPositionORDERBYJobPositionDESC;

InthischapteryouhavelearnthowtoencodeprogramminglinesusingthemostcommonlyusedDQLcommandstatementsinselecting,orderingandgroupingrecordsfromdatabasetablesinSQL.Inthenextchapteryouwilllearnthedifferenttransactionalcontrolcommandsthatwillallowyoutomanageseveralrelationaldatabasetransactions.

ChapterEight:TransactionalControlCommands

Inthischapteryouwilllearnhowtousethreeoftheavailabletransactionalcontrolcommandsinarelationaldatabasemanagementsystem(RDBMS)usingSQLiteStudio–COMMIT,ROLLBACKandSAVEPOINT.Controllingtransactionsrequiresyoutobeabletomanagecertaindatabasechangesthatareusuallybroughtaboutbytheinsert,updateanddeletecommands.

Executingadatabasetransactionseemstohavebeensuccessfullycompletedwhenyounoticethatthetable’sdataorstructurehasbeenchanged.Whatisactuallyhappeningduringatransactionexecutionisthatinformationisstoredinatemporaryspaceinthedatabase(orwhatyoucancallarollbackarea).Whenyouwanttofinalizethesetransactionsandstoretheinformationpermanently,thenyoueithersaveordiscardthechangesmadetothedatabasetablesbyissuingtheappropriatetransactionalcontrolcommand.Onlythenthattherollbackareaisemptied.

COMMITCommand

UsingtheCOMMITcommandsavesallthetransactionsintoyourdatabase.Normally,inSQLiteStudio,wheneveryouexecuteaCREATE,INSERTorDELETEtransactionbywritingprogramminglinesintheSQLEditor,thechangesareautomaticallysaved.YouhavefirstencounteredtheCOMMITcommandthroughtheCOMMITCHANGESSTRUCTUREbuttoninChapter6,whereyoucreatedacopyoftheCustomer_TBLtable.Now,todemonstratethiscommandagaininSQLiteStudio,youwillmanipulatethetablestructurebyaddinganewrecordtotheCustomer_TBLtableinGRIDVIEWmode.

1. Clickthe option.Toensurethatthereareno

transactionscurrentlyrunninginthedatabase,typethefollowingprogramminglineintheQUERYtabthenclicktheEXECUTEQUERY

button :

ENDTRANSACTION;

2. Double-clickCustomer_TBLundertheTABLESlistintheDATABASENAVIGATORpane.ClicktheDATAtabattherightandmakesurethattheGRIDViewisdisplayed.YouwillseealltherecordsoftheCustomer_TBLtable.

3. Clickthefirstcolumnofthelastrowofthetable,whichisCustomerID5.

4. Clickthedrop-downarrowbesidetheINSERTROW(INS)buttonandselectPLACENEWROWSBELOWSELECTEDROWoption.

5. ThistimeclicktheINSERTROW(INS)buttonandyouwillseeanewemptyrowaddedtothetable.

6. Addthefollowingdatavaluesinthenewrecord:

CustomerID:6CustomerName:JOHNDEPPJobPosition:PresidentCompanyName:RockersMineCompanyUSState:TXContactNo:3467654321

7. ClicktheCOMMITbutton topermanentlysavethenewdatavaluesaddedtothetable.

ROLLBACKCommand

IftheCOMMITcommandsavesallthechangestothedatabase,theROLLBACKcommandisthereversewherealltheunsavedchangeswillbediscarded.However,youcanonlyundotransactionssincethelastCOMMITorROLLBACKstatementexecuted.Thestandardsyntaxforthistransactionalcontrolcommandis:

ROLLBACK[WORK];

Also,beforeyoucanperformaROLLBACKcommand,makesurethattransactionshavestarted.Thismeansthatyouneedtoexecutethefollowingprogrammingstatementattheverybeginning:

BEGINTRANSACTION;

TodemonstratehowaROLLBACKstatementworks,youwillmodifytheDROPTABLEcommandinSQLiteStudio:

1. Clickthe option.IntheQUERYtab,typethefollowing

programmingstatementandclicktheEXECUTEQUERYbutton :

BEGINTRANSACTION;

2. Clickthe optionandcleartheQUERYtab.Typethe

followingandthenclicktheEXECUTEQUERYbutton .YouwillnoticethattheCustomer_TBLtableisnowremovedfromtheTableslist.

DROPTABLECustomer_TBL;

3. Clickthe optionagainandcleartheQUERYtab.Type

thefollowingandthenclicktheEXECUTEQUERYbutton :

ROLLBACK;

4. TocheckiftheROLLBACKcommandreversedthedeletionoftheCustomer_TBLtable,right-clickanywhereinsidetheDATABASENAVIGATORpane.ChooseREFRESHALLDATABASESCHEMASoption.

5. ClicktheTABLElistattheleftpane.YoushouldnowseethattheCustomer_TBLtableisbackundertheTABLElist.

SAVEPOINTCommand

Whenyouwanttoreversethetransactionjustbacktoacertainpointand

nottheentiretransaction,thenyouhavetoexecutetheSAVEPOINTcommandbeforeperformingaROLLBACKaction.ThisishowyoumanageseveraltransactionsintosmallergroupsofSQLcommands.Thestandardsyntaxforthistransactionalcontrolcommandis:

SAVEPOINTSAVEPOINT_NAME;

WhenusingtheSAVEPOINTandtheROLLBACKcommandstogether,thesyntaxis:

ROLLBACKTOSAVEPOINT_NAME;

Asavepointnamecanbethesameasthedatabaseobject’snametowhichyouwillbeperformingtheSQLtransactions.However,youshouldremembertomakethemunique,differentfromthegroupoftransactionsthatyouwanttobreakdownintoseveralpointsorsegments.

TodemonstratehowaSAVEPOINTwithaROLLBACKcommandworks,youwilldeletecertainrecordsfromtheCustomer_TBLtableandreversethistransaction.

1.Clickthe option.IntheQUERYtab,typethefollowingprogrammingstatementandclicktheEXECUTEQUERY

button :

BEGINTRANSACTION;

2.Clickthe optionagainandcleartheQUERYtab.Thentypethefollowing:

SAVEPOINTCustomer_SP1;

ClicktheEXECUTEQUERYbutton .AsavepointsectioniscreatedbeforedeletingthelastrecordoftheCustomer_TBLtable.

3.TodeletethelastrecordoftheCustomer_TBLtable,clickthe

optionandcleartheQUERYtab.Typethefollowingand

thenclicktheEXECUTEQUERYbutton :

DELETEFROMCustomer_TBLWHERECustomerID=6;

4.Tocheckiftherecordwasdeleted,double-clickCustomer_TBLundertheTABLESlistintheDATABASENAVIGATORpanethenclicktheDATAtabattheright.UndertheGRIDVIEWtab,clickthe

REFRESHTABLEDATAbutton orpressF5onyourkeyboard.Yourtableshouldbethesameasthefollowing:

5.Tocreatethesecondsavepointsection,clickthe optionagain.CleartheQUERYtabandthentypethefollowing:

SAVEPOINTCustomer_SP2;

ClicktheEXECUTEQUERYbutton .ThistimeasavepointsectioniscreatedbeforedeletingtherecordwheretheCustomerIDisequalto5.

6.TodeletetherecordwheretheCustomerIDisequalto5,clickthe

optionagainandcleartheQUERYtab.Typethefollowing

andclicktheEXECUTEQUERYbutton :

DELETEFROMCustomer_TBLWHERECustomerID=5;

7.Tocheckiftherecordwasdeleted,clickthe

optionatthebottomleftcornerofthescreenthenclicktheDATAtabattheright.UndertheGRIDVIEWtab,clicktheREFRESHTABLE

DATAbutton orpressF5.Yourtableshouldbethesameasthefollowing:

8.Toreversethelasttransactiondone,clickthe optionagainandcleartheQUERYtab.Typethefollowingandthenclickthe

EXECUTEQUERYbutton :

ROLLBACKTOCustomer_SP2;

9.Tocheckiftherecorddeletionwasreversed,clickthe

optionandthenclicktheDATAtabattheright.Under

theGRIDVIEWtab,clicktheREFRESHTABLEDATAbutton orpressF5.Yourtableshouldbethesameastheonebelow:

10.Toundothefirstrecorddeleted,clicktheoptionagainandcleartheQUERYtab.Typethefollowingandthenclick

theEXECUTEQUERYbutton :

ROLLBACKTOCustomer_SP1;

1.Tocheckiftherecorddeletionwasreversed,clickthe

optionandthenclicktheDATAtabattheright.UndertheGRIDVIEWtab,clicktheREFRESHTABLEDATAbutton

orpressF5.Yourtableshouldbethesameastheonebelow:

InthischapteryouhavelearnttheprimaryfunctionsofthethreetransactionalcontrolcommandsinsavingordiscardingchangesinanSQLdatabase.InthenextchapteryouwilllearntheimportanceofviewsandhowtomanipulatethemusingCREATE,UPDATEandDROPcommands.

ChapterNine:DatabaseViews

InthischapteryouwilllearnwhatadatabaseviewisanditsimportanceinSQLprogramming.Inaddition,youwillbeabletoperformtheexistingSQLcommandsincreating,updatinganddroppingviews.

DefiningViewsAviewisadatabaseobjectformedwhenyourSELECTqueriesaresavedinthedatabaseforfutureuse.Thismeansthataviewexistsbecauseofthetableswhereitsdatavalueswerederivedfrom.Thus,oneormoretablescancreateadatabaseview.Also,ithasthesamecharacteristicssimilartotheactualtableexceptthatyoudon’tneedsomephysicalspacetostoreit(temporarilysavedinthecomputer’smemory).Moreover,beingavirtualtable,youcannotmodifyitsdatavalues.

WhenexecutingaSELECTstatementtocreatetheview,youcaneithergetthecolumnnamesfromaparticulartableorperformcertainfunctionsandcalculationsthatwillmanipulatethegivendatavalues.Oncecreated,theseviewscanperformanyofthefollowingtasks:

Simplifydataretrieval-Someendusersmaynothavetheknowledgetoperformdatabaseoperationstogetthequeryresulttheyneed.Sotomakethingseasier,youcancreatedifferentviewsfromthetablesthatusersrequire.

Implementdatabasesecurity–Therearetimesthatyouhavetorestrictcertainusersonwhattheycanaccessfromyourdatabase,whethertheyareallowedtomodifydataorjustviewinformation.Toensurethatthetablesaresecured,youcangenerateviewsthatonlydisplaythedatavaluesthatyouallowuserstoaccess.

Supportdatasummarizationandreportgeneration–Throughviews,youareabletoturnacomplicatedSELECTqueryintoasimplesummarized

datathatyoucangeneratefrommultipletables.Thissummaryorreportcouldbegeneratedandupdatedfromtimetotime.Thatiswhyinsteadofcomposingcomplexprogramminglinesyoucanjustuseaggregatefunctionsincorporatedinthecreationofviews.

CreatingViewsTheSQLstatementCREATEVIEWisusedingeneratingviewsfromoneormoretables,andevenfromanotherview.Thefollowingisthemostbasicsyntaxusedincreatingaviewfromasingletable:CREATEVIEWVIEW_NAMEAS

SELECTCOLUMN_LISTFROMTABLE_NAME;

CreatingaViewfromtheEntireContentofaSingleTable

Forthisexercise,youwillbeusingtheCustomer_TBLtableoftheSample_DBdatabasetocreateaCustomer_VWviewinSQLiteStudio.

1. Clickthe optionanddeleteeverythinginsidetheQUERYtab.Thentypethefollowinglinesofcode:

CREATEVIEWCustomer_VWASSELECT*FROMCustomer_TBL;

2. ClicktheEXECUTEQUERYbutton ontopoftheQUERYtab.YouwillnownoticethatthereisaCustomer_VWviewundertheVIEWSsection,insidetheDATABASENAVIGATORpane.

3. Tocheckthecontentoftheview,double-clickCustomer_VWintheleftpanethentheDATAtabinSQLWORKAREA.TheCustomer_VWviewshouldcontainalltherecordsoftheCustomer_TBLtable.

CreatingaViewfromSelectedColumnsofaSingleTable

Ifyouwanttocreateaviewthatcontainsonlythecontactdetailsofthecustomer(CustomerName,CompanyNameandContactNo),thenyouwillselectcertaincolumnsfromtheCustomer_TBLtable.

1. Clickthe optionanddeleteeverythinginsidetheQUERYtab.Thentypethefollowinglinesofcode:

CREATEVIEWCustContactDeatails_VWASSELECTCustomerName,CompanyName,ContactNoFROM

Customer_TBL;Youneedtoprovideadifferentnameforthisnewview.SQLiteStudiowillnotallowyoutocreateanewviewwiththesamenameasanexistingview.

2. ClicktheEXECUTEQUERYbutton ontopoftheQUERYtab.YouwillnownoticethatthereisaCustContactDetails_VWviewundertheVIEWSsection,justontopoftheCustomer_VWview.TheVIEWSlistisalphabeticallyarrangedinascendingorder.

3. Tocheckthecontentofthisnewlycreatedview,double-click

CustContactDetails_VWintheleftpanethenclicktheDATAtabagain.Thisviewshouldcontainonlythreecolumns,namelyCustomerName,CompanyNameandContactNo,fromtheCustomer_TBLtable.

CreatingaViewfromMultipleTables

Whenyourequiremultipledatabasetablestocreatetheviewyouneed,ensurethatthetablesinvolvedwillhavetobejoinedbycolumnsthatarecommontothem.Forexample,youmayhaveanothertablethatcontainsinformationonthecustomers’orderssuchasthedatewhentheyordered,whatproducttheyordered,thequantityandmore.ThisnewtablewillbecalledtheORDERTABLEanditisrelatedtothefirstCUSTOMERTABLEbecauseeveryorderisassociatedtoaparticularcustomer.

Now,youwillcreateaviewfromtwotablesthatwillshowdatabaseuserstowhichcompanyandstateeachorderwasshippedtoordelivered.Thebasicsyntaxforcreatingaviewusingmultipletablesis:CREATEVIEWVIEW_NAMEAS

SELECTCOLUMN_LISTFROMTABLE_LISTWHERECONDITION;TocreatetheORDERTABLE:

1. UsingthedatavaluesinChapter2fortheORDERtable,create

anothertableusingtheSQLEditor.ClicktheoptionanddeleteeverythinginsidetheQUERYtab.TypethefollowinglinesofcodeforthenewORDERtable:

CREATETABLEOrder_TBL

(OrderIDINTEGERNOTNULLPRIMARYKEY,OrderDateDATENOTNULL,CustomerIDINTEGERNOTNULL,ProductIDINTEGERNOTNULL,OrderQtyBIGINTEGERNOTNULL);

2. ClicktheEXECUTEQUERYbutton ontopoftheQUERYtab.YouwillnowhavetheOrder_TBLtableundertheTABLES

listintheleftpane.

3. Double-clicktheOrder_TBLintheleftpanethenclickonDATAtabattheleft.YouwillpopulatethistablewithdatavaluesinGRIDVIEWmode.

4. ClicktheINSERTROWbutton andthenselectthefirstoption–INSERTMULTIPLEROWS.

5. Enter“4”intheNUMBEROFROWSTOINSERTinputbox(sincethereare4recordsintheORDERTABLEfromChapter2)thenclickOK.

6. TheOrder_TBLtablewillnowhave4rowsand5columns.InsteadofusingSQLstatementstopopulatethistable,youwillenterthevaluesdirectlyintothetable(checkthedatavaluesinChapter2).

7. ClicktheCOMMITbutton tosaveallthedatavaluesoftheOrder_TBLtable.

Tocreatetheviewthatwilltellyoutowhichcompanyandstateeveryorderwasshippedtoordelivered:

1. Clickthe option,emptyQUERYtabandthentypethefollowinglinesofcode:

CREATEVIEWOrderDelivery_VWASSELECTOrder_TBL.OrderID,Customer_TBL.CompanyNameASCompanyDeliveredTo,Customer_TBL.USStateASStateDestination,Order_TBL.OrderQtyFROMCustomer_TBL,Order_TBLWHEREOrder_TBL.CustomerID=

Customer_TBL.CustomerID;

2. ClicktheEXECUTEQUERYbutton ontopoftheQUERYtab.YouwillnowhaveanewviewnamedOrderDelivery_VW.

3. Tocheckthecontentofthisview,double-clickOrderDelivery_VWintheleftpanethenclicktheDATAtabattheright.

Inthisview,twocolumnswereselectedandrenamedfromtheCustomer_TBLtable-CompanyNamechangedtoCompanyDeliveredToandUSStatechangedtoStateDestination.TheothertwowerefromOrder_TBLtable—OrderIDandOrderQty(theoriginalcolumnnameswereretained).TherowsretrievedfrombothtablesarethoserecordswheretheCustomerIDoftheCustomer_TBLtablematchestheCustomerIDoftheOrder_TBLtable.

DroppingViewsTheDROPVIEWcommandisthestatementusedtodestroyanexistingviewfromthedatabase.Thebasicsyntaxis:DROPVIEWVIEW_NAME;TodropordeletetheentireCustomer_VWview:

1. Clickthe option,emptyQUERYtabandthentypethefollowinglinesofcode:

DROPVIEWCustomer_VW;

2. ClicktheEXECUTEQUERYbutton ontopoftheQUERYtab.YouwillnoticethattheCustomer_VWviewisalreadydeletedfromtheViewslist.

InthischapteryouhavelearntthedefinitionandimportanceofdatabaseviewsinSQL.Youhavealsoperformedcommonoperationsinmanipulatingviews,suchascreatinganddroppingthem.Inthenextchapteryouwilllearnmorein-depthconceptsindesigningdatabasesinSQL–primaryandforeignkeys,indexesandnormalizeddatabases.

ChapterTen:EnhancingDatabaseDesigns

Inthischapteryouwillgainmorein-depthknowledgeonenhancingdatabasedesignswiththeuseofprimaryandforeignkeys,indexesandnormalizationtechniques.Havingabetterunderstandingofdesigningdatabaseswillprovidethesoftwareapplicationyouareusinganedgebyperformingqueriesmoreeffectivelyandmaintainingdataintegrityatalltimes.

AssigningPrimaryandForeignKeysItisoneofthebestpracticestoassignaprimarykeywhenyoudefineadatabasetable.Inarelationaldatabase,theprimarykeyisaspecialfieldorcombinationoffieldsthatmakeeachrecordinthetableunique.Sincethepresenceoftheprimarykeydoesnotpermittheduplicationofvaluesonthecolumntowhichitwasassigned,thendataintegrityisguaranteed.Also,fieldsthataredesignatedasprimarykeyscannotcontainnullvalues.Definingaprimarykey,whetheritisexplicitorimplied,occursduringtablecreation.Normally,thetableswithprimarykeysareregardedasparenttables,meaningthesetablesprovideinformationtoanothertableorwhatistermedasthechildtable.Consequently,childtablesaredependentontheparenttable.

Inthepreviouschapters,youhavebeendealingwiththeCUSTOMERtableandtheORDERTable.WhatifyouhaveanothertablecalledthePRODUCTTablethatcontainsthefollowingfieldsorcolumns:ProductID,ProductNameandPriceperUnit?Youwillhavethefollowingrelationshipfrom

thesethreetables:

Fromthefigureabove,theCUSTOMER_TBLandthePRODUCT_TBLaretheparenttablesofthechildtableORDER_TBL(thisdescribesaparent-childrelationshipindatabasedesign).Asyoucansee,thefieldsnamedCustomerIDandProductIDaretheprimarykeysoftheparenttables.Thesetwofieldsarealsopresentinthechildtable.TheynowbecomeforeignkeysoftheORDER_TBLtable.Inotherwords,aforeignkeyisacolumnorfieldpresentinthechildtablethatreferencestotheprimarykeyofitsparenttable.

Unliketheprimarykey,aforeignkeydoesnotneedtobeuniqueallthetime.Inaddition,thenameoftheforeignkeycouldbedifferentfromthenameoftheprimarykeythatitreferencesto.Furthermore,theProductIDoftheparenttable(PRODUCT_TBL)canneverhaveduplicateentries,butnotthecorrespondingProductIDinthechildtable(ORDER_TBL).However,youshouldnotdefineandcreateaforeignkeyvalueifthereisnomatchingprimarykeyvalue.

UnderstandingIndexes

Whenadatabasestartstoslowdown,specificallyitsSQLqueries,youcan

createandimplementindexestoimproveitsperformance.Suchindexesareimportantobjectsthatserveaspointersassociatedtothedataofaparticulartable.Theprimaryfunctionofanindexistodeterminetheexactphysicallocationofthedatawhenaqueryisexecutedtoimproveitsretrievalprocess.Itworkslikeabook’salphabeticallyarrangedindexthathelpsyoufindtheinformationyouneedinamucheasierwayusingitspagenumbers.Thus,timeissaved,sinceyoudonotneedtoscanonerowatatime(mostespeciallyinextremelylargedatabases)andjustgodirectlytotherequiredrecord.

Thestoragespacesofanindexandthetablefromwhichitwascreatedareseparate.Suchallocatedphysicalspacecanalsoincreasetremendously,evenlargerthanthetableitreferences.Thatiswhystoragerequirementsaretakenintoconsiderationwhendesigningdatabases.Justliketablesandviews,indexescanalsobecreatedordropped.Whendesignedcorrectly,theyactuallyspeedupSELECTqueriesbutcouldslowdownDELETE,UPDATEandINSERTstatements.Forenormousdatabases,dataretrievalwilldefinitelyconsumesomuchtime.However,suchindextransactionshavenoeffectonthetable’sdata.

CreatingIndexes

Anindexisassociatedtoaparticularcolumnwhenitiscreated.Itthenholdsthelocationofthedatavaluesofthetablethatcontainsthatparticularindexedcolumn.Whenevernewdataisaddedtothetable,itwillalsobeaddedtotheindex.Let’ssayyouexecuteaSELECTstatementwithacertainconditionspecifiedintheWHEREclausethatchecksthecolumnthatisindexed.Thefirstthingthatwillhappenisthattheindexisfirstsearchedandwillonlyreturntheexactlocationifthedatavalueisfound.

Forexample,youwantedtoselectalltherecordsfromtheORDERtablewheretheCustomerIDmatchesto1.Youwillthenissuethefollowingquery:SELECT*

FROMOrder_TBLWHERECustomerID=1;IftheORDER_TBLtableisindexedon

theCustomerIDcolumn,thentherecordswillbearrangedinanascendingorderbasedonthatcolumn.Thus,theCustomerIDindexmakesiteasierforthesearchprocesstotakeplaceandfinallyresolvesthelocationofallthedatawiththematchingCustomerID.Oncethelocationisdetermined,thecorrespondingrowsofdatawillberetrievedfromtheORDER_TBLtable.Withouttheexistenceoftheindex,afullscanwillbeperformed,whichwillnotbeefficientifthetablecontainshundredsoreventhousandsofrecords.

Thebasicsyntaxisforcreatinganindexis:CREATEINDEXINDEX_NAMEONTABLE_NAME[(COLUMN_NAME)];Thisstatementcanvarybyaddingspecificationssuchasthecolumnnametobeindexed,ordering(whetherascendingordescending)andmanymore.Now,tocreatetheColumnIDindexoftheORDER_TBLtableinSQLiteStudio:

1. Clickthe optionandmakesuretheQUERYtabisempty.Thentypethefollowing:

CREATEINDEXCustomerID_IDXONOrder_TBL

(CustomerID);

2. ClicktheEXECUTEQUERYbutton ontopoftheQUERYtab.YouwillnowhaveCustomerID_IDXundertheINDEXESlistintheOrder_TBLtable.

DroppingIndexes

Justlikedroppingatableoraview,youwillusethefollowingbasicsyntax:DROPINDEXINDEX_NAME;Rememberthatyoucanre-

createtheindexafterithasbeendeleted,butmakesureyoutakeextraprecautionwhenperformingsuchtransactions.Also,whenyoudeleteatable,youwillalsobedeletingallthecorrespondingindexeswithit.Sometimesyoumayonlyneedtodeletetheindexandretainthetable.Suchimplementationhappenswhenyouonlywanttofixanindexproblemtooptimizethedatabaseperformanceandreducefragmentation.

Todroptheindexthatwehavecreatedpreviously:

1. Clickthe optionandmakesuretheQUERYtabisempty.Thentypethefollowing:

DROPINDEXCustomerID_IDX;

2. ClicktheEXECUTEQUERYbutton ontopoftheQUERYtab.YouwillnownoticethattheCustomerID_IDXindexhasbeendeletedfromtheIndexeslist.

NormalizingDatabases

Whydoyouneedtonormalizeadatabase?Thisisbecauseindesigningadatabaseyouneedtoensurethatinformationiswellorganized,easilymanaged,alwaysaccurateandthereisnounnecessaryduplication.Basically,normalizationistheprocessofdesigningandredesigningadatabasebyreducingonebigtableintotwosmallertables,wherethesametypeofdataaregroupedtogether.Forexample,ifyouonlyhaveonetablebymergingthecustomerinformationoftheCUSTOMER_TBLtablewiththeORDER_TBLtable,thenyouwillgetatablethatisnotnormalized:ORDER

IDORDERDATE

CUSTOMERID

NAME POSITION COMPANY STATE CONTACTNO

PRODUCTID

1 2016-05-23

1 KathyAle

TX 3461234567 4

2 2016-09-09

1 KathyAle

TX 3461234567 5

3 2016-02-17

3 KimAsh

`Director CarWorld CA 5101234567 2

4 2016-05-12

2 KevinLord

VP BestTooling

NY 5181234567 2

Asyoucansee,thereisaredundancyofdataonthepartofstoringthecustomerinformation.Thatiswhyitiswaybettertodividethistableintotwo

smalleronesthroughthenormalizationprocess.Alwaysbearinmindtokeepdataredundancytoaminimum,ifpossible,tosavestoragespaceandavoidinformationconfusion.Ifyouhavecustomerinformationforeverytableandonetabledoesnotmatchsuchinformationwithanother,thenhowwillyoubeabletoverifywhichoneiscorrect?Ifyouhavetoupdateacustomeraddress,thenyouarerequiredtoupdatethedatainallofthetableswhereitisincluded.Thus,timeandeffortinmanagingthedatabaseiswasted.

Thewayofmeasuringthedepthorleveltowhichadatabasehasbeennormalizediscalledanormalform.Therearethreecommonnormalforms,whereeachformisdependentonthepreviousnormalizationstepsperformedonthedatabase.

FirstNormalForm(1NF)

Givenasetofbasedata,thefirstnormalform(1NF)aimstodividethisintologicalunitsortablesofrelatedinformationwithanassignedprimarykey.Everycellcontainedinanyofthe2-dimensionaltablesshouldonlyhaveasinglevalue.Eachrowofaparticulartablereferstoacertainrecordofinformationandmustalwaysbeunique.Asforthecolumn,itisgivenauniquenameandconsistsofdatavaluesofthesametype,whichpertainstoasingleattributeoftheinformationcontainedinthetable.Moreover,thereisnoparticularorderthatthecolumnsnortherowsshouldbearranged.

ModifyingthegivendatabaseinChapter2byaddingemployeeinformation,youwillhavethefollowingbasedataforthecompany:

Basedfromthefigureabove,theentirecompanydatabasewasdividedintotwosmallertables–EMPLOYEE_TBLandCUSTOMER_TBL.TheprimarykeyforthesetablesareEmployeeIDandCustomerIDrespectively.Inthisway,itiseasiertoreadandmanagetheinformationascomparedtoonebigtablewithsomanycolumnsandrows.Thedatavaluesstoredineachtablerefertotwoseparateentities,meaningthosepiecesofinformationdescribingthecompany’semployeesareonlypresentintheEMPLOYEE_TBLtablewhilethosethatonlypertaintothecustomersarestoredintheCUSTOMER_TBLtable.

SecondNormalForm(2NF)

Afteryouaredonewiththefirstnormalform,thenextstepisderivingthesecondnormalform(2NF).Thisprocessfocusesonfunctionaldependencythatdescribestherelationshipsbetweenattributes.Whenanattributedeterminesthevalueofanother,thenthereisfunctionaldependencybetweenthem.Inthiscase,youwillstoredatavaluesfromtheEmployeeandCustomertablesthatarepartlydependentontheirprimarykeysintoseparatetables.

ThefigureaboveshowsthatthoseattributesthatarepartlydependentontheEmployeeIDprimarykeyhavebeenremovedfromEMPLOYEE_TBLandstoredinanewtablecalledEMPLOYEE_SALARY_TBL.Theattributesthatwereretainedintheoriginaltablearefullydependentontheprimarykey–meaningthatforeveryrecordoflastname,firstname,addressandcontractnumberthereisacorrespondingparticularemployeeID.UnliketheEMPLOYEE_SALARY_TBL,aparticularemployeeIDdoesnotreferenceauniqueemployeepositionnorsalaryrate.Therecouldbemorethanoneemployeewiththesameposition(EmpPosition),payrate(Payrate)andbonus(Bonus).

FortheCUSTOMER_TBLtable,customer’sorderinformationdoesnotdirectlydependonthegeneralcustomerinformationfoundintheoriginaltable.Thatiswhyfourattributes(OrderID,OrderDate,ProductIDandOrderQty)weremovedtoaseparatetablecalledORDER_TBL.

ThirdNormalForm(3NF)

Withthethirdnormalform(3NF),youwillhavetoseparatepiecesofinformationfromthetablethatarecompletelynotdependentontheprimarykey.GoingbacktotheCUSTOMER_TBL,thejobposition(JobPosition)anditsdescription(JobDescription)aretotallyindependentoftheCustomerIDprimarykey.Thisisbecause,ingeneral,anyjobpositionwillhavethesamedutiesandresponsibilitiesregardlessofwhothecustomeris.Thus,wewillseparatetheJobPositionandJobDescriptionattributesintoanothertablecalledPOSITION_TBL.

Inthischapteryouhavelearntthattherearedesignpracticesthatyoucanapplytoboosttheperformanceofyourdatabases.Duplicatedatavaluesareavoidedbyassigningprimaryandforeignkeysintables.Searchqueriesareheightenedthroughtheimplementationoftableindexes.Dataconsistencyandsecurityareimprovedbecauseofthenormalizationprocess.Thus,overalldatabaseorganizationisenhanced.InthenextchapteryouwilllearnsomeadvancetopicsinSQLdesignthatincludescursors,triggersanderrors.

ChapterEleven:DatabaseAdvanceTopics

InthischapteryouwillbeintroducedtosomeadvancetopicsinSQLthatgoesbeyondbasicdatabasetransactions.Evenifthissectiononlyincludesanoverviewofcursors,triggersanderrors,suchknowledgecouldpossiblyhelpyouextendthefeaturesofyourSQLimplementations.

Cursors

Generally,SQLcommandsmanipulatedatabaseobjectsusingset-basedoperations.Thismeansthattransactionsareperformedonagrouporblockofdata.Acursor,ontheotherhand,processesdatafromatableonerowatatime.Itiscreatedusingacompoundastatementanddestroyeduponexit.Thestandardsyntaxfordeclaringacursoris(whichmaydifferforeveryimplementation):

DECLARECURSORCURSOR_NAMEIS{SELECT_STATEMENT}

Youcanperformoperationsonacursoronlyafterithasbeendeclaredordefined.

OpenaCursor

Oncedeclared,youperformanOPENoperationtoaccessthecursorandthenexecutethespecifiedSELECTstatement.TheresultsoftheSELECTquerywillbesavedinacertainareainthememory.Thestandardsyntaxforopeningacursoris:

OPENCURSOR_NAME;

FetchDatafromaCursor

TheFETCHstatementisperformedifyouwanttoretrievethequeryresultsorthedatafromthecursor.Thestandardsyntaxforfetchingdatais:

FETCHNEXTFROMCURSOR_NAME[INTOFETCH_LIST]

InSQLprogramming,theoptionalstatementinsidethesquarebracketswillletyouassignthedataretrievedintoacertainvariable.

CloseaCursor

ThereisacorrespondingCLOSEstatementtobeexecutedwhenyouopenaparticularcursor.Oncethecursorisclosed,allthenamesandresourcesusedwillbedeallocated.Thus,thecursorisnolongeravailablefortheprogramtouse.Thestandardsyntaxforclosingacursoris:

CLOSECURSOR_NAME

Triggers

ThereareinstanceswhenyouwantcertainSQLoperationsortransactionstooccurafterperformingsomespecificactions.ThisscenariodescribesanSQLstatementthattriggersanotherSQLstatementtotakeplace.Essentially,atriggerisanSQLprocedurethatiscompiledinthedatabasethatexecutecertaintransactionsbasedonothertransactionsthathavepreviouslyoccurred.SuchtriggerscanbeperformedbeforeoraftertheexecutionofDMLstatements

(INSERT,DELETEandUPDATE).Inaddition,triggerscanvalidatedataintegrity,maintaindataconsistency,undotransactions,logoperations,modifyandreaddatavaluesindifferentdatabases.

CreateaTrigger

Thestandardsyntaxforcreatingatriggeris:

CREATETRIGGERTRIGGER_NAMETRIGGER_ACTION_TIMETRIGGER_EVENT

ONTABLE_NAME[REFERENCINGOLD_OR_NEW_VALUE_ALIAS_LIST]TRIGGERED_ACTION

TRIGGER_NAME-theuniqueidentifyingnameforthisobject

TRIGGER_ACTION_TIMETRIGGER_EVENT-thespecifiedtimethatthesetoftriggeredactionswilloccur(whetherbeforeorafterthetriggeringevent).

TABLE_NAME–thetableforwhichtheDMLstatementshavebeenspecified

TRIGGERED_ACTION–specifiestheactionstobeperformedonceaneventistriggered

Onceatriggerhasbeencreated,itcannotbealteredanymore.Youcanjust

eitherre-createorreplaceit.Howatriggerworksdependswhatconditionsyouspecify–whetheritwillfireatoncewhenaDMLstatementisperformedoritwillfiremultipletimesforeverytablerowaffectedbytheDMLstatement.YoucanalsoincludeathresholdvalueoraBooleancondition,thatwhensuchconditionismetwilltriggeracourseofaction.

DropaTrigger

Thebasicsyntaxfordroppingatriggeristhesameasdroppingatableoraview:

DROPTRIGGERTRIGGER_NAME;

Errors

Anerror-freedesignorimplementationisoneoftheultimategoalsinanyprogramminglanguage.Youcancommiterrorsbysimplynotfollowingnamingconventions,improperlywritingtheprogrammingcodes(syntaxortypoerrorslikeamissingapostropheorparenthesis)orevenwhenthedataentereddoesnotmatchthedatatypedefined.

Tomakethingseasier,SQLhasdevisedawaytoreturnerrorinformationsothatprogrammerswillbeawareofwhatisgoingonandbeabletoundertaketheappropriateactionstocorrectthesituation.Someoftheseerror-handlingmechanismsarethestatusparameterSQLSTATEandtheWHENEVERclause.

SQLSTATE

ThestatusparameterorhostvariableSQLSTATEisanerror-handlingtoolthatincludesawideselectionofanomalouscondition.Itisastringthatconsistsoffivecharacters(uppercaselettersfromAtoZandnumeralsfrom0to9),wherethefirsttwocharactersrefertotheclasscodewhilethenextthreeisthesubclasscode.TheclasscodeidentifiesthestatusafteranSQLstatementhasbeencompleted–whetheritissuccessfulornot(ifnotsuccessful,thenoneofthemajortypesoferrorconditionsarereturned).SupplementaryinformationabouttheexecutionoftheSQLstatementisalsoindicatedinthesubclasscode.

TheSQLSTATEisupdatedaftereveryoperation.Ifthevalueis‘00000’(fivezeroes),itmeansthattheexecutionwassuccessfulandyou

canproceedtothenextoperation.Ifitcontainsafive-characterstringotherthan‘00000’,thenyouhavetocheckyourprogramminglinestorectifytheerrorcommitted.TherearenumerouswaysonhowtohandleacertainSQLerror,dependingontheclasscodeandsubclasscodespecifiedintheSQLSTATE.

WHENEVERClause

TheWHENEVERclauseerror-handlingmechanismfocusesonexecutionexceptions.Withthis,anerrorisacknowledgedandgivestheprogrammertheoptiontocorrectit.Thisisbetterthannotbeingabletodosomethingifanerroroccurs.Ifyoucannotrectifyorreversetheerrorthatwascommitted,thenyoucanjustgracefullyterminatetheapplicationprogram.

TheWHENEVERclauseiswrittenbeforetheexecutableSQLcode,specificallyintheSQLdeclarationsection.Thebasicsyntaxis:

WHENEVERCONDITIONACTION;

CONDITION–valuecaneitherbeSQLERROR(returnsTRUEifSQLSTATEclasscodeisotherthan00,01or02)orNOTFOUND(returnsTRUEifSQLSTATEis02000)

ACTION–valuecaneitherbeCONTINUE(executionoftheprogramiscontinuednormally)orGOTOaddress(executionofadesignatedprogramaddress)

Inthischapteryouhavelearnttheprimaryroleofcursors,howtriggersworkandtheimportanceofhandlingerrorsinSQLprogramming.LearningtheseadvancetopicsisonestepcloserinmaximizingthepotentialsofyourSQLimplementations.

ChapterTwelve:Exercises

Exercise#1

CreateaninvoicetablenamedOrderInvoice_TBLinSQLiteStudiowiththefollowingfields:InvoiceID–primarykey,integerdatatypeCustomerID–integerdatatypeOrderID–integerdatatypeTaxAmt–decimaldatatypewithaprecisionof9andascaleof2

TotalSaleAmt–decimaldatatypewithaprecisionof9andascaleof2

ShippingFee–decimaldatatypewithaprecisionof9andascaleof2

Exercise#2

AftercreatingtheOrderInvoicetable,populatethefieldsusingtheINSERTstatementwiththefollowingdatavalues:

InvoiceID CustomerID

OrderID TaxAmount

TotalSales

ShippingFee

2016001 1 1005

$523.80 $198023.05

$1981.78

2016002 3 1006

$302.83 $198302.03

$2005.10

2016003 3 1007

$217.02 $20021.70

$1983.12

2016004 2 1008

$909.00 $200009.09

$19827.22

Exercise#3

CreateaviewnamedOrderLargeSales_VWfromOrderInvoicetablewherethetotalsalesisgreaterthan$150,000.00andthetaxamountislessthan$600.Theviewwillonlyconsistofthefollowingfields:CustomerID,OrderID,TaxAmountandTotalSales.

Exercise#4

DeletetheOrderInvoice_TBLtableandtheOrderInv_VWviewusingtheDMLcommandDROP.

ExerciseAnswers

AnswersforExercise#1

1. LaunchSQLiteStudio.ClickonTOOLSmenuandthenchooseOPENSQLEDITORoption.

2. ClicktheQUERYtabattherightandtypethefollowingprogramminglines:CREATETABLEOrderInvoice_TBL(InvoiceIDINTEGERPRIMARYKEY,CustomerIDINTEGER,OrderIDINTEGER,TaxAmtDECIMAL(9,2),TotalSaleAmtDECIMAL(9,2),ShippingFeeDECIMAL(9,2));

2. ClicktheQUERYtabattherightandtypethefollowingprogramminglines:INSERTINTOOrderInvoice_TBLVALUES(2016001,1,1005,523.80,198023.05,1981.78),(2016002,3,1006,302.83,198302.03,2005.10),(2016003,3,1007,217.02,20021.70,1983.12),(2016004,2,1008,909.00,200009.09,19827.22);

2. ClicktheQUERYtabattherightandtypethefollowingprogramminglines:CREATEVIEWOrderInv_VWAS

SELECTCustomerID,OrderID,TaxAmt,TotalSaleAmtFROMOrderInvoice_TBLWHERETotalSaleAmt>150000ANDTaxAmt<600;

2. ClicktheQUERYtabattherightandtypethefollowingprogramming

linestodeletethetable:DROPTABLEOrderInvoice_TBL;

4. Todeletetheview,typethefollowingprogramminglinesandthen

clicktheEXECUTEQUERYbutton .DROPVIEWOrderInv_VW;

Hereisaquickrecapofwhatwecoveredincaseyouneedarefresheronacertainstep:

1. YounowhaveanunderstandingofthehistoryandusesoftheSQL

language.2. Youlearnthowtodescriberelationaldatabasesanddatabasemanagement

systems.3. YoulearnthowtousethedifferentSQLcommandtypesandinstall

SQLiteStudio.4. Youlearnthowtodefineandusethevariousdatatypes.5. YoulearnthowtousetheCREATE,ALTERandDROPstatements.6. YoulearnthowtousetheINSERT,UPDATEandDELETEstatements.7. YoulearnthowtousetheSELECT,WHERE,ORDERBYandGROUP

BYstatements.8. YoulearnthowtousetheCOMMIT,ROLLBACKandSAVEPOINT

commands.9. Youalsolearnthowtodefine,createanddropviews.

10.Youlearnthowtoassignprimaryandforeignkeys,createindexesandnormalizedatabases.11.Youlearnthowtousecursors,triggersanderrors.

FinalWords

IhopethatyouhavetrulyenjoyedlearningtheessentialsofSQLprogramminganddatabasemanagementusingSQLiteStudiothroughthiseBook.IhadmadesurethatyouwilltremendouslybenefitfromreadingthisbymeetingyourgoalsinunderstandingwhatSQLdatabaseisatanaffordableprice.IamsurethatwiththeknowledgeyouhavegainedthroughtheguidelinesofthiseBook,youcannowplan,designandcreateyourveryowndatabasesinSQLiteStudio.

Youmayalsoconsiderlearningotherprogramminglanguages,yourknowledgeofSQLProgrammingwillgiveyouatremendousadvantageifyouwishtolearnotherlanguages.YoucanfindotherpopularprogrammingbooksHERE.

Bytheway,Iwouldgreatlyappreciateifyoucanprovideanyconstructivefeedbackorreviewsthatwillfurtherimprovemyskillsasawriter.Pleasefeelfreetosendmeanemail,especiallyifyouhaveanythingtoclarifyorask(evenifyoujustwanttodropbyandsayhello!).MyemailaddressisFelix_Alvaro@mail.com.

Again,thankyouandGodblessalways!

FelixAlvaro

sql: easy sql programming & database management for beginners, your step-by-step guide to...

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