programming the database -...

Hacettepe UniversityComputerEngineeringDepartment

ProgrammingtheDatabase

BBM471DatabaseManagementSystems

Dr.Fuat Akal

[email protected]

Hacettepe UniversityComputerEngineeringDepartmentHacettepe UniversityComputerEngineeringDepartment

Today’sLecture

1. StoredProcedures

2. Functions

3. Cursors

4. Triggers

5. DynamicSQL

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StoredProcedures

• AstoredprocedurecontainsasequenceofSQLcommandsstoredinthedatabasecatalogsothatitcanbeinvokedlaterbyaprogram

• Storedproceduresaredeclaredusingthefollowingsyntax(IrefertoMySQLinthispresentation):

CreateProcedure <proc-name>(param_spec1,param_spec2,…,param_specn )

begin-- executioncode

end;

whereeachparam_spec isoftheform:[in|out|inout]<param_name><param_type>

• inmode:allowsyoutopassvaluesintotheprocedure,• outmode:allowsyoutopassvaluebackfromproceduretothecallingprogram


ExampleStoredProcedure:Definition

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Supposewewanttokeeptrackofthetotalsalariesofemployeesworkingforeachdepartment

Weneedtowriteaproceduretoupdatethesalariesinthedeptsal table


CreatetheStoredProcedure

1. Changethedelimiter(i.e.,terminatingcharacter)ofSQLstatementfromsemicolon(;)tosomethingelse(e.g.,//)

2. DefineaprocedurecalledupdateSalary whichtakesasinputadepartmentnumber.

3. ThebodyoftheprocedureisanSQLcommandtoupdatethetotalsalary columnofthedeptsal table.

4. Terminatetheproceduredefinitionusingthedelimiteryouhaddefinedinstep1(//)

5. Changethedelimiterbacktosemicolon(;)

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CalltheStoredProcedure

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DebuggingaStoredProcedure

• Usingaselectstatement• SELECT ‘Comment’; -- PuttheliteralCommentouttoconsole

• Insertintoatable• Puttingthecurrenttimeanddatestampintoacolumnwiththecomment.

• Logmessagestoanoutputfile• Select <time_stamp>, ‘Comment’ into outfile ‘<file_name>’;

• Whichmightbeblockedbythesecuritymechanism.

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ProgrammingStructures

• Googlefor“XXXreferencemanual”• XXXàMySQL,SQLServer,Oracle,Sybase,etc.

• e.g.,tolocateIFstatement,clickon• FunctionsandOperators

• ControlFlowFunctions

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https://dev.mysql.com/doc/refman/8.0/en/


DatabaseCursors

• Adatabasecursor isacontrolstructurethatenablestraversalovertherecordsinadatabase.

• Cursors facilitatesubsequentprocessinginconjunctionwiththetraversal,suchasretrieval,additionandremovalofdatabase records.

• Acursor can'tbeusedbyitself.Itisanessentialcomponentinstoredprocedures.

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ExampleCursor

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Drop the old procedure

Use cursor to iterate the rows


CursorExample(OraclePl/SQL)

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DECLAREPi constant NUMBER(8,7) := 3.1415926;area NUMBER(14,2);cursor rad_cursor is select * from RAD_VALS;rad_val rad_cursor%ROWTYPE;

BEGINopen rad_cursor;fetch rad_cursor into rad_val;area:=pi*power(rad_val.radius,2);insert into AREAS values (rad_val.radius, area);close rad_cursor;

END;

Rad_cursor

fetch

Rad_val

Radius AreaAREAS

3 28.27

VALSRAD_

radius

3

6

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SelectForUpdate

• Cursorscanalsobeusedtoperformupdates

cursor<cname>is<select-statement>forupdate;

• Selectstatementshouldinvolveonlyonedatabasetable

update<table-name>set<set-clause>wherecurrentof<cname>;

deletefrom<table-name>wherecurrentof<cname>;

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Functions

• Functionsreturnsomevalueandaredeclaredusingthefollowingsyntax:

function <function-name>(param_spec1,…,param_speck)

returns<return_type>[not]deterministic

Begin-- executioncode

end;

whereparam_spec is:

[in|out|inout]<param_name><param_type>

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ExampleFunction

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FunctionCall

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Hacettepe UniversityComputerEngineeringDepartment

Triggers


WhatisaTrigger?

• Atrigger isastatementthatisexecutedautomaticallybythesystemasasideeffectofamodificationtothedatabase.

• Todesignatriggermechanism,wemust:• Specifytheconditionsunderwhichthetriggeristobeexecuted.• Specifytheactionstobetakenwhenthetriggerexecutes.

• TriggersintroducedtoSQLstandardinSQL:1999,butsupportedevenearlierusingnon-standardsyntaxbymostdatabases.

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Triggervs.Vendors

• AvailableinmostenterpriseDBMSs(Oracle,IBMDB2,MSSQLserver)andsomepublicdomainDBMSs(Postgres,MySQL)

• SomevendorDBMSpermitnativeextensionstoSQLforspecifyingthetriggers• e.g.PL/SQLinOracle,TransactSQLinMSSQLServer

• SomeDBMSalsoallowuseofgeneralpurposeprogramminglanguageinsteadofSQL

• e.g.JavainOracle,C#/VBinSQLServer

• SomeDBMSextendthetriggersbeyondtables• forexamplealsotoviewsasinOracle

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TypesofTriggers

• Howmanytimesshouldthetriggerbodyexecutewhenthetriggeringeventtakesplace?

• Perstatement: thetriggerbodyexecutesonceforthetriggeringevent.Thisisthedefault.

• Foreachrow: thetriggerbodyexecutesonceforeachrowaffectedbythetriggeringevent.

• Whenthetriggercanbefired• RelativetotheexecutionofanSQLDMLstatement(beforeorafterorinsteadofit)

• Exactlyinasituationdependingonspecificsystemresources(e.g.signalfromthesystemclock,expiringtimer,exhaustingmemory)

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TriggeringEventsandActionsinSQL

• Triggeringeventcanbeinsert,delete orupdate

• Valuesofattributesbeforeandafteranupdatecanbereferenced• referencingoldrowas :fordeletesandupdates• referencingnewrowas:forinsertsandupdates

• Triggerscanbeactivatedbeforeanevent,whichcanserveasextraconstraints.E.g.convertblankstonull.

createtriggersetnull-triggerbeforeupdateonrreferencingnewrowasnrowforeachrowwhennrow.phone-number=‘‘setnrow.phone-number=null

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FiringSequenceofDatabaseTriggersonaSingleRow

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DEPTNO10203040

DNAMEACCOUNTINGRESEARCHSALESOPERATIONS

LOCNEW YORKDALLASCHICAGOBOSTON

DEPT table BEFORE statement trigger

BEFORE row triggerAFTER row trigger

AFTER statement trigger


FiringSequenceofDatabaseTriggersonMultipleRows

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EMPNO

7839

7698

7788

ENAME

KING

BLAKE

SMITH

DEPTNO

30

30

30

BEFORE statement trigger

BEFORE row triggerAFTER row triggerBEFORE row triggerAFTER row triggerBEFORE row triggerAFTER row trigger

AFTER statement trigger

EMP table


TriggerExample- 1

• Wewanttocreateatriggertoupdatethetotalsalaryofadepartmentwhenanewemployeeishired

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TriggerExample- 1

• Createatriggertoupdatethetotalsalaryofadepartmentwhenanewemployeeishired

• Thekeyword“new”referstothenewrowinserted

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Hacettepe UniversityComputerEngineeringDepartmentHacettepe UniversityComputerEngineeringDepartment 25

totalsalary increases by 90K

totalsalary did not change

TriggerExample- 1


TriggerExample- 2

• Atriggertoupdatethetotalsalaryofadepartmentwhenanemployeetupleismodified:

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TriggerExample- 2

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TriggerExample- 3

• Atriggertoupdatethetotalsalaryofadepartmentwhenanemployeetupleisdeleted:

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TriggerExample- 3

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UsingDatabaseTriggersforInformationProcessing

• AuditingTableOperations• eachtimeatableisaccessedauditinginformationisrecordedagainstit

• TrackingRecordValueChanges• eachtimearecordvalueischangedthepreviousvalueisrecorded

• ProtectingDatabaseReferentialIntegrity:ifforeignkeypointstochangingrecords• referentialintegritymustbemaintained

• MaintenanceofSemanticIntegrity• e.g.whenthefactoryisclosed,allemployeesshouldbecomeunemployed

• StoringDerivedData• e.g.thenumberofitemsinthetrolleyshouldcorrespondtothecurrentsessionselection

• SecurityAccessControl• e.g.checkinguserprivilegeswhenaccessingsensitiveinformation

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WhenNotToUseTriggers

• Triggerswereusedearlierfortaskssuchas• maintainingsummarydata(e.g.totalsalaryofeachdepartment)• Replicatingdatabasesbyrecordingchangestospecialrelations(calledchange ordeltarelations)andhavingaseparateprocessthatappliesthechangesovertoareplica

• Therearebetterwaysofdoingthesenow:• Databasestodayprovidebuiltinmaterializedviewfacilitiestomaintainsummarydata• Databasesprovidebuilt-insupportforreplication

• Encapsulationfacilitiescanbeusedinsteadoftriggersinmanycases• Definemethodstoupdatefields• Carryoutactionsaspartoftheupdatemethodsinsteadofthroughatrigger

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DynamicSQL

Sometimesyouneedtooperateagainstatableorcolumnsthatarenotknownatcompiletime.

CREATE DEFINER=`root`@`localhost` PROCEDURE `dynamic`(in tableName varchar(40))begin

set @statement = concat('select * from ', tableName);prepare stmt from @statement;execute stmt;set @statement = concat('select count(*) from ', tableName, ' into @count');prepare stmt from @statement;execute stmt;select concat('Count was: ', @count, ' from table: ', tableName);deallocate prepare stmt;

end

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Summary

• ItisnotpossibletoperformalltasksbyusingasingleSQLstatement

• Sometimesyouneedtoimplementthebusinesslogicatthedatabaseside

• Thereyoucanusestoredprocedures,functions,cursors,trigger,etc.• Therearefewmorestructuresnotcoveredinthislecture

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Acknowledgements

Thecoursematerialusedforthislectureismostlytakenand/oradoptedfrom:

• www.cse.msu.edu/~pramanik/teaching/courses/cse480/14s/lectures/12/lecture13.pptbySaktiPramanik atMichiganStateUniversity

• DatabaseSystemConcepts,Avi Silberschatz,HenryF.Korth,S.Sudarshan

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