Top 100 SQL Interview Questions and Answers

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SQL
TOP 100
INTERVIEW QUESTIONS & ANSWERS

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WhatisDBMS?
2
QUESTION
ADatabaseManagementSystem(DBMS)isaprogramthatcontrolscreation,maintenanceanduseofadatabase. DBMScanbetermedasFileManagerthatmanagesdatainadatabaseratherthansavingitinfilesystems.
ANSWER
QUESTION 1

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WhatisRDBMS?
3
QUESTION
RDBMSstandsforRelationalDatabaseManagementSystem.RDBMSstorethedataintothecollectionoftables, whichisrelatedbycommonfieldsbetweenthecolumnsofthetable.Italsoprovidesrelationaloperatorstomanipulatethedatastoredintothetables.
Example:SQLServer.
ANSWER
QUESTION 2

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WhatisSQL?
4
QUESTION
SQLstandsforStructuredQueryLanguage,anditisusedtocommunicatewiththeDatabase.Thisisastandardlanguageusedtoperformtaskssuchasretrieval,updation,insertionanddeletionofdatafromadatabase.
StandardSQLCommandsareSelect.
ANSWER
QUESTION 3

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WhatisaDatabase?
5
QUESTION
Databaseisnothingbutanorganizedformofdataforeasyaccess,storing,retrievalandmanagingofdata.Thisisalsoknownasstructuredformofdatawhichcanbeaccessedinmanyways.
Example:SchoolManagementDatabase,BankManagementDatabase.
ANSWER
QUESTION 4

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WhataretablesandFields?
6
QUESTION
AtableisasetofdatathatareorganizedinamodelwithColumnsandRows.Columnscanbecategorizedasvertical,andRowsarehorizontal.Atablehasspecifiednumberofcolumncalledfieldsbutcanhaveanynumberofrowswhichiscalledrecord.
Example:.
Table:Employee.
Field:EmpID,EmpName,DateofBirth.
Data:201456,David,11/15/1960.
ANSWER
QUESTION 5

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Whatisaprimarykey?
7
QUESTION
Aprimarykeyisacombinationoffieldswhichuniquelyspecifyarow.Thisisaspecialkindofuniquekey,andithasimplicitNOTNULLconstraint.Itmeans,PrimarykeyvaluescannotbeNULL.
ANSWER
QUESTION 6

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Whatisauniquekey?
8
QUESTION
AUniquekeyconstraintuniquelyidentifiedeachrecordinthedatabase.Thisprovidesuniquenessforthecolumnorsetofcolumns.
APrimarykeyconstrainthasautomaticuniqueconstraintdefinedonit.Butnot,inthecaseofUniqueKey.
Therecanbemanyuniqueconstraintdefinedpertable,butonlyonePrimarykeyconstraintdefinedpertable.
ANSWER
QUESTION 7

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Whatisaforeignkey?
9
QUESTION
Aforeignkeyisonetablewhichcanberelatedtotheprimarykeyofanothertable.Relationshipneedstobecreatedbetweentwotablesbyreferencingforeignkeywiththeprimarykeyofanothertable.
ANSWER
QUESTION 8

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Whatarethetypesofjoinandexplaineach?
10
QUESTION
Therearevarioustypesofjoinwhichcanbeusedtoretrievedataanditdependsontherelationshipbetweentables.
InnerJoin:Innerjoinreturnrowswhenthereisatleastonematchofrowsbetweenthetables.
RightJoin:RightjoinreturnrowswhicharecommonbetweenthetablesandallrowsofRighthandsidetable. Simply,itreturnsalltherowsfromtherighthandsidetableeventhoughtherearenomatchesinthelefthandsidetable.
LeftJoin:LeftjoinreturnrowswhicharecommonbetweenthetablesandallrowsofLefthandsidetable.Simply,itreturnsalltherowsfromLefthandsidetableeventhoughtherearenomatchesintheRighthandsidetable.
FullJoin:Fulljoinreturnrowswhentherearematchingrowsinanyoneofthetables.Thismeans,itreturnsalltherowsfromthelefthandsidetableandalltherowsfromtherighthandsidetable.
ANSWER
QUESTION 9

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Explainanouterjoin?
11
QUESTION
Anouterjoinincludesrowsfromtableswhentherearenomatchingvaluesinthetables.
ANSWER
QUESTION 10

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Whatisnormalization?
12
QUESTION
Normalizationistheprocessofminimizingredundancyanddependencybyorganizingfieldsandtableofadatabase.ThemainaimofNormalizationistoadd,deleteormodifyfieldthatcanbemadeinasingletable.
ANSWER
QUESTION 11

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WhatisDenormalization?
13
QUESTION
DeNormalizationisatechniqueusedtoaccessthedatafromhighertolowernormalformsofdatabase.Itisalsoprocessofintroducingredundancyintoatablebyincorporatingdatafromtherelatedtables.
ANSWER
QUESTION 12

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Whatareallthedifferentnormalizations?
14
QUESTION
Thenormalformscanbedividedinto4forms,andtheyareexplainedbelow-.
FirstNormalForm(1NF):Thisshouldremovealltheduplicatecolumnsfromthetable.Creationoftablesfortherelateddataandidentificationofuniquecolumns.
SecondNormalForm(2NF):Meetingallrequirementsofthefirstnormalform.PlacingthesubsetsofdatainseparatetablesandCreationofrelationshipsbetweenthetablesusingprimarykeys.
ThirdNormalForm(3NF):Thisshouldmeetallrequirementsof2NF.Removingthecolumnswhicharenotdependentonprimarykeyconstraints.
FourthNormalForm(4NF):Meetingalltherequirementsofthirdnormalformanditshouldnothavemulti- valueddependencies.
ANSWER
QUESTION 13

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WhatisanIndex?Whatareallthedifferenttypesofindexes?
15
QUESTION
Anindexisperformancetuningmethodofallowingfasterretrievalofrecordsfromthetable.Anindexcreatesanentryforeachvalueanditwillbefastertoretrievedata.
Thisindexingdoesnotallowthefieldtohaveduplicatevaluesifthecolumnisuniqueindexed.Uniqueindexcanbeappliedautomaticallywhenprimarykeyisdefined.
ClusteredIndex:Thistypeofindexreordersthephysicalorderofthetableandsearchbasedonthekeyvalues. Eachtablecanhaveonlyoneclusteredindex.
NonClusteredIndex:NonClusteredIndexdoesnotalterthephysicalorderofthetableandmaintainslogicalorderofdata.Eachtablecanhave999nonclusteredindexes.
ANSWER
QUESTION 14

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Whatisarelationshipandwhatarethey?
16
QUESTION
DatabaseRelationshipisdefinedastheconnectionbetweenthetablesinadatabase.Therearevariousdatabasingrelationships,andtheyareasfollows:. OnetoOneRelationship. OnetoManyRelationship. ManytoOneRelationship. Self-ReferencingRelationship.
ANSWER
QUESTION 15

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Whatisaquery?
17
QUESTION
ADBqueryisacodewritteninordertogettheinformationbackfromthedatabase.Querycanbedesignedinsuchawaythatitmatchedwithourexpectationoftheresultset.Simply,aquestiontotheDatabase.
ANSWER
QUESTION 16

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Whatissubquery?Whatarethetypesofsubquery?
18
QUESTION
Asubqueryisaquerywithinanotherquery.Theouterqueryiscalledasmainquery,andinnerqueryiscalledsubquery.SubQueryisalwaysexecutedfirst,andtheresultofsubqueryispassedontothemainquery.
Therearetwotypesofsubquery–CorrelatedandNon-Correlated.
Acorrelatedsubquerycannotbeconsideredasindependentquery,butitcanreferthecolumninatablelistedintheFROMthelistofthemainquery.
ANon-Correlatedsubquerycanbeconsideredasindependentqueryandtheoutputofsubqueryaresubstitutedinthemainquery.
ANSWER
QUESTION 17

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Whatisatrigger?
19
QUESTION
ADBtriggerisacodeorprogramsthatautomaticallyexecutewithresponsetosomeeventonatableorviewinadatabase.Mainly,triggerhelpstomaintaintheintegrityofthedatabase.
Example:Whenanewstudentisaddedtothestudentdatabase,newrecordsshouldbecreatedintherelatedtableslikeExam,ScoreandAttendancetables.
ANSWER
QUESTION 18

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WhatarethetypesofTriggers?
20
QUESTION
Therearefourtypesoftriggersandtheyare:
•Insert
•Delete
•Update
•Insteadof
ANSWER
QUESTION 19

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WhatisthedifferencebetweenDELETETRUNCATEandDROPcommands?
21
QUESTION
DELETEcommandisusedtoremoverowsfromthetable,andWHEREclausecanbeusedforconditionalsetofparameters.CommitandRollbackcanbeperformedafterdeletestatement.
TRUNCATEremovesallrowsfromthetable.Truncateoperationcannotberolledback.
Dropcommandisusedtodropthetableorkeyslikeprimary,foreignfromatable.
ANSWER
QUESTION 20

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WhatisdataIntegrity?
22
QUESTION
DataIntegritydefinestheaccuracyandconsistencyofdatastoredinadatabase.Itcanalsodefineintegrityconstraintstoenforcebusinessrulesonthedatawhenitisenteredintotheapplicationordatabase.
ANSWER
QUESTION 21

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Whatiscollation?
23
QUESTION
Collationisdefinedassetofrulesthatdeterminehowcharacterdatacanbesortedandcompared.ThiscanbeusedtocompareAand,otherlanguagecharactersandalsodependsonthewidthofthecharacters.
ASCIIvaluecanbeusedtocomparethesecharacterdata.
ANSWER
QUESTION 22

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AdvantagesandDisadvantagesofStoredProcedure?
24
QUESTION
Storedprocedurecanbeusedasamodularprogramming–meanscreateonce,storeandcallforseveraltimeswheneverrequired.Thissupportsfasterexecutioninsteadofexecutingmultiplequeries.Thisreducesnetworktrafficandprovidesbettersecuritytothedata.
DisadvantageisthatitcanbeexecutedonlyintheDatabaseandutilizesmorememoryinthedatabaseserver.
ANSWER
QUESTION 23

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WhatisSQLInjection?
25
QUESTION
SQLInjectionisoneofthetechniquesusesbyhackerstohackawebsitebyinjectingSQLcommandsindatafields.
ANSWER
QUESTION 24

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WhatisthedifferencebetweenaHAVINGCLAUSEandaWHERECLAUSE?
26
QUESTION
Theyspecifyasearchconditionforagrouporanaggregate.ButthedifferenceisthatHAVINGcanbeusedonlywiththeSELECTstatement.HAVINGistypicallyusedinaGROUPBYclause.WhenGROUPBYisnotused, HAVINGbehaveslikeaWHEREclause.HavingClauseisbasicallyusedonlywiththeGROUPBYfunctioninaquerywhereasWHEREClauseisappliedtoeachrowbeforetheyarepartoftheGROUPBYfunctioninaquery.
ANSWER
QUESTION 25

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Howwouldapplydaterangefilter?
27
QUESTION
a.Youcanusesimplecondition>=and<=orsimilarorusebetween/andbutthetrickistoknowyourexactdatatype.
b.Sometimesdatefieldscontaintimeandthatiswherethequerycangowrongsoitisrecommendedtousesomedaterelatedfunctionstoremovethetimeissue.InSQLServercommonfunctiontodothatisdatedifffunction.
c.Youalsohavetobeawareofdifferenttimezonesandservertimezone.
d.Toincreasequeryperformanceyoumaystillwanttousebetweenhoweveryoushouldbeawareofproperformatyoushoulduseifnotitmightmisbehaveduringfiltering.
ANSWER
QUESTION 26

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WhatisthedifferencebetweenJOINandUNION?
28
QUESTION
SQLJOINallowsusto―lookup‖recordsonothertablebasedonthegivenconditionsbetweentwotables.Forexample,ifwehavethedepartmentIDofeachemployee,thenwecanusethisdepartmentIDoftheemployeetabletojoinwiththedepartmentIDofdepartmenttabletolookupdepartmentnames.
UNIONoperationallowsustoadd2similardatasetstocreateresultingdatasetthatcontainsallthedatafromthesourcedatasets.Uniondoesnotrequireanyconditionforjoining.Forexample,ifyouhave2employeetableswithsamestructure,youcanUNIONthemtocreateoneresultsetthatwillcontainalltheemployeesfrombothofthetables.
SELECT*FROMEMP1
UNION
SELECT*FROMEMP2;
ANSWER
QUESTION 27

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WhatisthedifferenceamongUNION,MINUSandINTERSECT?
29
QUESTION
UNIONcombinestheresultsfrom2tablesandeliminatesduplicaterecordsfromtheresultset.
MINUSoperatorwhenusedbetween2tables,givesusalltherowsfromthefirsttableexcepttherowswhicharepresentinthesecondtable.
INTERSECToperatorreturnsusonlythematchingorcommonrowsbetween2resultsets.
ANSWER
QUESTION 28

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WhatisSelfJoinandwhyisitrequired?
30
QUESTION
SelfJoinistheactofjoiningonetablewithitself.SelfJoinisoftenveryusefultoconvertahierarchicalstructureintoaflatstructure
ANSWER
QUESTION 29

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HowcanwetransposeatableusingSQL(changingrowstocolumnorvice-versa)?
31
QUESTION
TheusualwaytodoitinSQListouseCASEstatementorDECODEstatement.
ANSWER
QUESTION 30

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WhatarethedifferencesamongROWNUM,RANKandDENSE_RANK?
32
QUESTION
ROW_NUMBERassignscontiguous,uniquenumbersfrom1..Ntoaresultset.
RANKdoesnotassignuniquenumbers—nordoesitassigncontiguousnumbers.Iftworecordstieforsecondplace,norecordwillbeassignedthe3rdrankasnoonecameinthird,accordingtoRANK.
DENSE_RANK,likeRANK,doesnotassignuniquenumbers,butitdoesassigncontiguousnumbers.Eventhoughtworecordstiedforsecondplace,thereisathird-placerecord.
ANSWER
QUESTION 31

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Whatisadatabasetransaction?
33
QUESTION
Databasetransactiontakedatabasefromoneconsistentstatetoanother.Attheendofthetransactionthesystemmustbeinthepriorstateiftransactionfailsorthestatusofthesystemshouldreflectthesuccessfulcompletionifthetransactiongoesthrough.
ANSWER
QUESTION 32

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Whatarepropertiesofatransaction?
34
QUESTION
PropertiesofthetransactioncanbesummarizedasACIDProperties.
1.Atomicity:Atransactionconsistsofmanysteps.Whenallthestepsinatransactiongetscompleted,itwillgetreflectedinDBorifanystepfails,allthetransactionsarerolledback.
2.Consistency:Thedatabasewillmovefromoneconsistentstatetoanother,ifthetransactionsucceedsandremainintheoriginalstate,ifthetransactionfails.
3.Isolation:Everytransactionshouldoperateasifitistheonlytransactioninthesystem
4.Durability:Onceatransactionhascompletedsuccessfully,theupdatedrows/recordsmustbeavailableforallothertransactionsonapermanentbasis
ANSWER
QUESTION 33

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WhatisaDatabaseLock?Whatarethetypeoflocks?
35
QUESTION
Databaselocktellatransaction,ifthedataiteminquestionsiscurrentlybeingusedbyothertransactions.
1.SharedLock:Whenasharedlockisappliedondataitem,othertransactionscanonlyreadtheitem,butcan'twriteintoit.
2.ExclusiveLock:Whenaexclusivelockisappliedondataitem,othertransactionscan'treadorwriteintothedataitem.
ANSWER
QUESTION 34

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WhatisaCompositeKey?
36
QUESTION
ACompositeprimarykeyisatypeofcandidatekey,whichrepresentsasetofcolumnswhosevaluesuniquelyidentifyeveryrowinatable.
Forexample-if"Employee_ID"and"EmployeeName"inatableiscombinedtouniquelyidentifiesarowitscalledaCompositeKey.
ANSWER
QUESTION 35

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WhatisaCompositePrimaryKey?
37
QUESTION
ACompositeprimarykeyisasetofcolumnswhosevaluesuniquelyidentifyeveryrowinatable.Whatitmeansisthat,tablewhichcontainscompositeprimarykeywillbeindexedbasedoncolumnsspecifiedintheprimarykey. ThiskeywillbereferredinForeignKeytables.
Forexample-ifcombinedeffectofcolumns,"Employee_ID"and"EmployeeName"inatableisrequiredtouniquelyidentifiesarow,itscalledaCompositePrimaryKey.Inthiscase,boththecolumnswillberepresentedasprimarykey.
ANSWER
QUESTION 36

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DefineSQLInsertStatement?
38
QUESTION
SQLINSERTstatementisusedtoaddrowstoatable.Forafullrowinsert,SQLQueryshouldstartwith―insertinto―statementfollowedbytablenameandvaluescommand,followedbythevaluesthatneedtobeinsertedintothetable.Insertcanbeusedinseveralways:
1.Toinsertasinglecompleterow
2.Toinsertasinglepartialrow
ANSWER
QUESTION 37

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DefineSQLUpdateStatement?
39
QUESTION
SQLUpdateisusedtoupdatedatainaroworsetofrowsspecifiedinthefiltercondition.
ThebasicformatofanSQLUPDATEstatementis,UpdatecommandfollowedbytabletobeupdatedandSETcommandfollowedbycolumnnamesandtheirnewvaluesfollowedbyfilterconditionthatdetermineswhichrowsshouldbeupdated.
ANSWER
QUESTION 38

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WhatarewildcardsusedindatabaseforPatternMatching?
40
QUESTION
SQLLikeoperatorisuserforpatternmatching.SQL'Like'commandtakesmoretimetoprocess.Sobeforeusinglikeoperator,considersuggestionsgivenbelowonwhenandwheretousewildcardsearch.
1)Don'toverusewildcards.Ifanothersearchoperatorwilldo,useitinstead.
2)Whenyoudousewildcards,trynottousethematthebeginningofthesearchpattern,unlessabsolutelynecessary.Searchpatternsthatbeginwithwildcardsaretheslowesttoprocess.
3)Paycarefulattentiontotheplacementofthewildcardsymbols.Iftheyaremisplaced,youmightnotreturnthedatayouintended
ANSWER
QUESTION 39

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WhatisCrossJoin?
41
QUESTION
CrossJoinwillreturnallrecordswhereeachrowfromthefirsttableiscombinedwitheachrowfromthesecondtable.
ANSWER
QUESTION 40

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Whatisaview?
42
QUESTION
Viewsarevirtualtables.Unliketablesthatcontaindata,viewssimplycontainqueriesthatdynamicallyretrievedatawhenused.
ANSWER
QUESTION 41

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Whatisamaterializedview?
43
QUESTION
Materializedviewsisalsoaviewbutarediskbased.Materializedviewsgetupdatedonspecificduration,baseupontheintervalspecifiedinthequerydefinition.Wecanindexmaterializedview.
ANSWER
QUESTION 42

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Whataretheadvantagesanddisadvantagesofviewsinadatabase?
44
QUESTION
Advantages:
1.Viewsdoesn'tstoredatainaphysicallocation.
2.Viewcanbeusetohidesomeofthecolumnsfromthetable
3.ViewscanprovideAccessRestriction,sincedatainsertion,updateanddeletionisnotpossibleontheview.
Disadvantages:
1.Whenatableisdropped,associatedviewbecomeirrelevant.
2.Sinceviewarecreatedwhenaqueryrequestingdatafromviewistriggered,itsbitslow
3.Whenviewsarecreatedforlargetables,itoccupymorememory.
ANSWER
QUESTION 43

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WhendoyouuseUPDATE_STATISTICScommand?
45
QUESTION
Thiscommandisusedwhenalargeprocessingofdatahasoccurred.Ifanylargeamountofdeletions,anymodifications,orBulkCopyintothetableshasoccurred,ithastoupdatetheindexestotakethesechangesintoaccount.UPDATE_STATISTICSupdatestheindexesonthesetablesaccordingly.
ANSWER
QUESTION 44

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WhatisanIDENTITYcolumnininsertstatements?
46
QUESTION
IDENTITYcolumnisusedintablecolumnstomakethatcolumnasAutoincrementalnumberorasurrogatekey.
ANSWER
QUESTION 45

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HowwillIretrieveallrecordsofemployment1thoseshouldnotbepresentnemployment2?
47
QUESTION
(Select*fromemployment2)-(Select*fromemployment1).
ANSWER
QUESTION 46

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WhichTCP/IPportdoesSQLServerrunon?Howcanitbechanged?
48
QUESTION
SQLServerrunsonport1433.ItcanbechangedfromtheNetworkUtilityTCP/IPproperties.
ANSWER
QUESTION 47

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WhatisSQLServerAgent?
49
QUESTION
SQLServeragentplaysanimportantroleintheday-to-daytasksofadatabaseadministrator(DBA).ItspurposeistoeasetheimplementationoftasksfortheDBA,withitsfull-functionschedulingengine,whichallowsyoutoscheduleyourownjobsandscripts.
ANSWER
QUESTION 48

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WhichcommandusingQueryAnalyzerwillgiveyoutheversionofSQLserverandoperatingsystem?
50
QUESTION
SELECTSERVERPROPERTY('productversion'),SERVERPROPERTY('productlevel')andSERVERPROPERTY('edition')
ANSWER
QUESTION 49

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HowtocreaterecursivequeryinSQLServer?
51
QUESTION
RecursivequerycanbecreateinSQLusingstoredprocedurebutyoucanalsouseCTE(Commontableexpression).ItmightbealsoworthaskingaboutperformanceasCTEisnotalwaysveryfast.
ANSWER
QUESTION 51

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Whatisaconstraint?
52
QUESTION
Constraintcanbeusedtospecifythelimitonthedatatypeoftable.Constraintcanbespecifiedwhilecreatingoralteringthetablestatement.Sampleofconstraintare.
•NOTNULL.
•CHECK.
•DEFAULT.
•UNIQUE.
•PRIMARYKEY.
•FOREIGNKEY.
ANSWER
QUESTION 51

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WhatisAutoIncrement?
53
QUESTION
Autoincrementkeywordallowstheusertocreateauniquenumbertobegeneratedwhenanewrecordisinsertedintothetable.AUTOINCREMENTkeywordcanbeusedinOracleandIDENTITYkeywordcanbeusedinSQLSERVER.
MostlythiskeywordcanbeusedwheneverPRIMARYKEYisused.
ANSWER
QUESTION 52

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WhatisDatawarehouse?
54
QUESTION
Datawarehouseisacentralrepositoryofdatafrommultiplesourcesofinformation.Thosedataareconsolidated, transformedandmadeavailablefortheminingandonlineprocessing.WarehousedatahaveasubsetofdatacalledDataMarts.
ANSWER
QUESTION 53

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Whatisuserdefinedfunctions?
55
QUESTION
Userdefinedfunctionsarethefunctionswrittentousethatlogicwheneverrequired.Itisnotnecessarytowritethesamelogicseveraltimes.Instead,functioncanbecalledorexecutedwheneverneeded.
ANSWER
QUESTION 54

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Whatarealltypesofuserdefinedfunctions?
56
QUESTION
Threetypesofuserdefinedfunctionsare.
a.ScalarFunctions.
b.InlineTablevaluedfunctions.
c.Multistatementvaluedfunctions.
ANSWER
QUESTION 55

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Whatarealldifferenttypesofcollationsensitivity?
57
QUESTION
Followingaredifferenttypesofcollationsensitivity-.
•CaseSensitivity–AandaandBandb.
•AccentSensitivity.
•KanaSensitivity–JapaneseKanacharacters.
•WidthSensitivity–Singlebytecharacteranddoublebytecharacter.
ANSWER
QUESTION 56

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WhatisOnlineTransactionProcessing(OLTP)?
58
QUESTION
OnlineTransactionProcessingorOLTPmanagestransactionbasedapplicationswhichcanbeusedfordataentryandeasyretrievalprocessingofdata.Thisprocessingmakeslikeeasieronsimplicityandefficiency.Itisfaster, moreaccurateresultsandexpenseswithrespecttoOTLP.
Example–BankTransactionsonadailybasis.
ANSWER
QUESTION 57

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WhatisanALIAScommand?
59
QUESTION
ALIASnamecanbegiventoatableorcolumn.ThisaliasnamecanbereferredinWHEREclausetoidentifythetableorcolumn.
Example-.
Selectst.StudentID,Ex.Resultfromstudentst,ExamasExwherest.studentID=Ex.StudentID
Here,streferstoaliasnameforstudenttableandExreferstoaliasnameforexamtable.
ANSWER
QUESTION 58

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Whatareaggregateandscalarfunctions?
60
QUESTION
Aggregatefunctionsareusedtoevaluatemathematicalcalculationandreturnsinglevalues.Thiscanbecalculatedfromthecolumnsinatable.Scalarfunctionsreturnasinglevaluebasedontheinputvalue.
Example-.
Aggregate–max(),count–Calculatedwithrespecttonumeric.
Scalar–UCASE(),NOW()–Calculatedwithrespecttostrings.
ANSWER
QUESTION 59

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Howcanyoucreateanemptytablefromanexistingtable?
61
QUESTION
Select*intostudentcopyfromstudentwhere1=2
Here,wearecopyingstudenttabletoanothertablewiththesamestructurewithnorowscopied.
ANSWER
QUESTION 60

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Howtofetchcommonrecordsfromtwotables?
62
QUESTION
Commonrecordsresultsetcanbeachievedby-.
SelectstudentIDfromstudent.<strong>INTERSECT</strong>SelectStudentIDfromExam
ANSWER
QUESTION 61

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Howtoselectuniquerecordsfromatable?
63
QUESTION
SelectuniquerecordsfromatablebyusingDISTINCTkeyword.
SelectDISTINCTStudentID,StudentNamefromStudent.
ANSWER
QUESTION 62

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Whatarethedifferentindexconfigurationsatablecanhave?
64
QUESTION
Atablecanhaveoneofthefollowingindexconfigurations:
1.Noindexes
2.Aclusteredindex
3.Aclusteredindexandmanynonclusteredindexes
4.Anonclusteredindex
5.Manynonclusteredindexes
ANSWER
QUESTION 63

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WhatarethepropertiesanddifferentTypesofSub-Queries?
65
QUESTION
PropertiesofSub-Query
a.Asub-querymustbeenclosedintheparenthesis.
b.Asub-querymustbeputintherighthandofthecomparisonoperator,and
c.Asub-querycannotcontainanORDER-BYclause.
d.Aquerycancontainmorethanonesub-query.
TypesofSub-Query
e.Single-rowsub-query,wherethesub-queryreturnsonlyonerow.
f.Multiple-rowsub-query,wherethesub-queryreturnsmultiplerows,.and
g.Multiplecolumnsub-query,wherethesub-queryreturnsmultiplecolumns
ANSWER
QUESTION 64

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WhatisSQLProfiler?
66
QUESTION
SQLProfilerisagraphicaltoolthatallowssystemadministratorstomonitoreventsinaninstanceofMicrosoftSQLServer.YoucancaptureandsavedataabouteacheventtoafileorSQLServertabletoanalyzelater.Forexample,youcanmonitoraproductionenvironmenttoseewhichstoredproceduresarehamperingperformancesbyexecutingtooslowly.
UseSQLProfilertomonitoronlytheeventsinwhichyouareinterested.Iftracesarebecomingtoolarge,youcanfilterthembasedontheinformationyouwant,sothatonlyasubsetoftheeventdataiscollected.Monitoringtoomanyeventsaddsoverheadtotheserverandthemonitoringprocessandcancausethetracefileortracetabletogrowverylarge,especiallywhenthemonitoringprocesstakesplaceoveralongperiodoftime.
ANSWER
QUESTION 65

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WhataretheauthenticationmodesinSQLServer?Howcanitbechanged?
67
QUESTION
WindowsmodeandMixedMode-SQLandWindows.TochangeauthenticationmodeinSQLServerclickStart, Programs,MicrosoftSQLServerandclickSQLEnterpriseManagertorunSQLEnterpriseManagerfromtheMicrosoftSQLServerprogramgroup.SelecttheserverthenfromtheToolsmenuselectSQLServerConfigurationProperties,andchoosetheSecuritypage.
ANSWER
QUESTION 66

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Canastoredprocedurecallitselforrecursivestoredprocedure?HowmuchlevelSPnestingispossible?
68
QUESTION
Yes.BecauseTransact-SQLsupportsrecursion,youcanwritestoredproceduresthatcallthemselves.Recursioncanbedefinedasamethodofproblemsolvingwhereinthesolutionisarrivedatbyrepetitivelyapplyingittosubsetsoftheproblem.Acommonapplicationofrecursivelogicistoperformnumericcomputationsthatlendthemselvestorepetitiveevaluationbythesameprocessingsteps.StoredproceduresarenestedwhenonestoredprocedurecallsanotherorexecutesmanagedcodebyreferencingaCLRroutine,type,oraggregate.Youcanneststoredproceduresandmanagedcodereferencesupto32levels.
ANSWER
QUESTION 67

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WhatisLogShipping?
69
QUESTION
LogshippingistheprocessofautomatingthebackupofdatabaseandtransactionlogfilesonaproductionSQLserver,andthenrestoringthemontoastandbyserver.EnterpriseEditionsonlysupportslogshipping.Inlogshippingthetransactionallogfilefromoneserverisautomaticallyupdatedintothebackupdatabaseontheotherserver.Ifoneserverfails,theotherserverwillhavethesamedbandcanbeusedthisastheDisasterRecoveryplan.Thekeyfeatureoflogshippingisthatitwillautomaticallybackuptransactionlogsthroughoutthedayandautomaticallyrestorethemonthestandbyserveratdefinedinterval.
ANSWER
QUESTION 68

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Name3waystogetanaccuratecountofthenumberofrecordsinatable?
70
QUESTION
SELECT*FROMtable1
SELECTCOUNT(*)FROMtable1
SELECTrowsFROMsysindexesWHEREid=OBJECT_ID(table1)ANDindid<2
ANSWER
QUESTION 69

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WhatdoesitmeantohaveQUOTED_IDENTIFIERON?WhataretheimplicationsofhavingitOFF?
71
QUESTION
WhenSETQUOTED_IDENTIFIERisON,identifierscanbedelimitedbydoublequotationmarks,andliteralsmustbedelimitedbysinglequotationmarks.WhenSETQUOTED_IDENTIFIERisOFF,identifierscannotbequotedandmustfollowallTransact-SQLrulesforidentifiers.
ANSWER
QUESTION 70

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WhatisthedifferencebetweenaLocalandaGlobaltemporarytable?
72
QUESTION
1.Alocaltemporarytableexistsonlyforthedurationofaconnectionor,ifdefinedinsideacompoundstatement,forthedurationofthecompoundstatement.
2.Aglobaltemporarytableremainsinthedatabasepermanently,buttherowsexistonlywithinagivenconnection. Whenconnectionisclosed,thedataintheglobaltemporarytabledisappears.However,thetabledefinitionremainswiththedatabaseforaccesswhendatabaseisopenednexttime.
ANSWER
QUESTION 71

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HowGlobaltemporarytablesarerepresentedanditsscope?
73
QUESTION
Globaltemporarytablesarerepresentedwith##beforethetablename.Scopewillbetheoutsidethesessionwhereaslocaltemporarytablesareinsidethesession.SessionIDcanbefoundusing@@SPID.
ANSWER
QUESTION 72

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WhatistheSTUFFfunctionandhowdoesitdifferfromtheREPLACEfunction?
74
QUESTION
STUFFfunctionisusedtooverwriteexistingcharacters.Usingthissyntax,STUFF(string_expression,start,length, replacement_characters),string_expressionisthestringthatwillhavecharacterssubstituted,startisthestartingposition,lengthisthenumberofcharactersinthestringthataresubstituted,andreplacement_charactersarethenewcharactersinterjectedintothestring.REPLACEfunctiontoreplaceexistingcharactersofalloccurrences. UsingthesyntaxREPLACE(string_expression,search_string,replacement_string),whereeveryincidenceofsearch_stringfoundinthestring_expressionwillbereplacedwithreplacement_string.
ANSWER
QUESTION 73

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WhatisCHECKConstraint?
75
QUESTION
ACHECKconstraintisusedtolimitthevaluesthatcanbeplacedinacolumn.Thecheckconstraintsareusedtoenforcedomainintegrity.
ANSWER
QUESTION 74

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WhatisthedifferencebetweenUNIONandUNIONALL?
76
QUESTION
UNIONstatementismainlyusedtocombinethetablesincludingtheduplicaterowsandUNIONALLcombinebutdoesnotlookforduplicaterows.Withthis,UNIONALLwillbeveryfasterthanUNIONstatements.
ANSWER
QUESTION 75

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WhatisNOTNULLConstraint?
77
QUESTION
ANOTNULLconstraintenforcesthatthecolumnwillnotacceptnullvalues.Thenotnullconstraintsareusedtoenforcedomainintegrity,asthecheckconstraints.
ANSWER
QUESTION 76

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Howtoget@@ERRORand@@ROWCOUNTatthesametime?
78
QUESTION
If@@RowcountischeckedafterErrorcheckingstatementthenitwillhave0asthevalueof@@Recordcountasitwouldhavebeenreset.Andif@@Recordcountischeckedbeforetheerror-checkingstatementthen@@Errorwouldgetreset.Toget@@errorand@@rowcountatthesametimedobothinsamestatementandstoretheminlocalvariable.
SELECT@RC=@@ROWCOUNT,@ER=@@ERROR
ANSWER
QUESTION 77

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WhatisaScheduledJobsorWhatisaScheduledTasks?
79
QUESTION
Scheduledtasksletuserautomateprocessesthatrunonregularorpredictablecycles.Usercanscheduleadministrativetasks,suchascubeprocessing,torunduringtimesofslowbusinessactivity.UsercanalsodeterminetheorderinwhichtasksrunbycreatingjobstepswithinaSQLServerAgentjob.E.g.backupdatabase,UpdateStatsofTables.Jobstepsgiveusercontroloverflowofexecution.Ifonejobfails,usercanconfigureSQLServerAgenttocontinuetoruntheremainingtasksortostopexecution.
ANSWER
QUESTION 78

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Whatisatablecalled,ifithasneitherClusternorNon-clusterIndex?Whatisitusedfor?
80
QUESTION
UnindexedtableorHeap.MicrosoftPressBooksandBookonLine(BOL)refersitasHeap.Aheapisatablethatdoesnothaveaclusteredindexand,therefore,thepagesarenotlinkedbypointers.TheIAMpagesaretheonlystructuresthatlinkthepagesinatabletogether.Unindexedtablesaregoodforfaststoringofdata.Manytimesitisbettertodropallindexesfromtableandthendobulkofinsertsandtorestorethoseindexesafterthat.
ANSWER
QUESTION 79

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CanSQLServerslinkedtootherserverslikeOracle?
81
QUESTION
SQLServercanbelinkedtoanyserverprovidedithasOLE-DBproviderfromMicrosofttoallowalink.E.g.OraclehasanOLE-DBproviderfororaclethatMicrosoftprovidestoadditaslinkedservertoSQLServergroup.
ANSWER
QUESTION 80

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WhatisBCP?Whendoesitused?
82
QUESTION
BulkCopyisatoolusedtocopyhugeamountofdatafromtablesandviews.BCPdoesnotcopythestructuressameassourcetodestination.BULKINSERTcommandhelpstoimportadatafileintoadatabasetableorviewinauser-specifiedformat.
ANSWER
QUESTION 81

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Howtoimplementone-to-one,one-to-manyandmany-to-manyrelationshipswhiledesigningtables?
83
QUESTION
One-to-Onerelationshipcanbeimplementedasasingletableandrarelyastwotableswithprimaryandforeignkeyrelationships.One-to-Manyrelationshipsareimplementedbysplittingthedataintotwotableswithprimarykeyandforeignkeyrelationships.Many-to-Manyrelationshipsareimplementedusingajunctiontablewiththekeysfromboththetablesformingthecompositeprimarykeyofthejunctiontable.
ANSWER
QUESTION 82

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Whatisanexecutionplan?Whenwouldyouuseit?Howwouldyouviewtheexecutionplan?
84
QUESTION
AnexecutionplanisbasicallyaroadmapthatgraphicallyortextuallyshowsthedataretrievalmethodschosenbytheSQLServerqueryoptimizerforastoredprocedureorad-hocqueryandisaveryusefultoolforadevelopertounderstandtheperformancecharacteristicsofaqueryorstoredproceduresincetheplanistheonethatSQLServerwillplaceinitscacheandusetoexecutethestoredprocedureorquery.FromwithinQueryAnalyzerisanoptioncalled"ShowExecutionPlan"(locatedontheQuerydrop-downmenu).Ifthisoptionisturnedonitwilldisplayqueryexecutionplaninseparatewindowwhenqueryisranagain.
ANSWER
QUESTION 83

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WhatarethetwoauthenticationmodesinSQLServer?
85
QUESTION
Therearetwoauthenticationmodes–
•WindowsMode
•MixedMode
ModescanbechangedbyselectingthetoolsmenuofSQLServerconfigurationpropertiesandchoosesecuritypage.
ANSWER
QUESTION 84

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WhatisCOALESCEinSQLServer?
86
QUESTION
COALESCEisusedtoreturnfirstnon-nullexpressionwithinthearguments.Thisfunctionisusedtoreturnanon- nullfrommorethanonecolumninthearguments.
Example–
SelectCOALESCE(empno,empname,salary)fromemployee;
ANSWER
QUESTION 85

hirist
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HowexceptionscanbehandledinSQLServerProgramming?
87
QUESTION
ExceptionsarehandledusingTRY—-CATCHconstructsanditishandlesbywritingscriptsinsidetheTRYblockanderrorhandlingintheCATCHblock.
ANSWER
QUESTION 86

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WhatisthepurposeofFLOORfunction?
88
QUESTION
FLOORfunctionisusedtoroundupanon-integervaluetothepreviousleastinteger.ExampleisgivenFLOOR(6.7)
Returns6.
ANSWER
QUESTION 87

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Canwechecklocksindatabase?Ifso,howcanwedothislockcheck?
89
QUESTION
Yes,wecanchecklocksinthedatabase.Itcanbeachievedbyusingin-builtstoredprocedurecalledsp_lock.
ANSWER
QUESTION 88

hirist
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WhatistheuseofSIGNfunction?
90
QUESTION
SIGNfunctionisusedtodeterminewhetherthenumberspecifiedisPositive,NegativeandZero.Thiswillreturn+1,-1or0.
Example:SIGN(-35)returns-1
ANSWER
QUESTION 89

hirist
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HowistheSUBSTRkeywordusedinSQL?
91
QUESTION
SUBSTRisusedforstringmanipulationwithcolumnname,firstpositionandstringlengthusedasarguments.E.g.
SUBSTR(NAME,13)referstothefirstthreecharactersinthecolumnNAME.
ANSWER
QUESTION 90

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WhatisaNULLvalue?WhataretheprosandconsofusingNULLS?
92
QUESTION
ANULLvaluetakesuponebyteofstorageandindicatesthatavalueisnotpresentasopposedtoaspaceorzerovalue.It'stheDB2equivalentofTBDonanorganizationalchartandoftencorrectlyportraysabusinesssituation. Unfortunately,itrequiresextracodingforanapplicationprogramtohandlethissituation.
ANSWER
QUESTION 91

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Whatisasynonym?Howisitused?
93
QUESTION
Asynonymisusedtoreferenceatableorviewbyanothername.Theothernamecanthenbewrittenintheapplicationcodepointingtotesttablesinthedevelopmentstageandtoproductionentitieswhenthecodeismigrated.ThesynonymislinkedtotheAUTHIDthatcreatedit.
ANSWER
QUESTION 92

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WhatisaCartesianproduct?
94
QUESTION
ACartesianproductresultsfromafaultyquery.Itisarowintheresultsforeverycombinationinthejointables.
ANSWER
QUESTION 93

hirist
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Whatisatuple?
95
QUESTION
StaticSQLiscompiledandoptimizedpriortoitsexecution;dynamiciscompiledandoptimizedduringexecution.
ANSWER
QUESTION 94

hirist
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Whatisreferentialintegrity?
96
QUESTION
Referentialintegrityreferstotheconsistencythatmustbemaintainedbetweenprimaryandforeignkeys,i.e.everyforeignkeyvaluemusthaveacorrespondingprimarykeyvalue.
ANSWER
QUESTION 95

hirist
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What’sthemaximumsizeofarow?
97
QUESTION
8060bytes.
ANSWER
QUESTION 96

hirist
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HowtochangeDatabasenameinSQLserver?
98
QUESTION
Usethefollowingcode:
SupportedinSQLserver2000and2005
Execsp_renamedb―test‖,―test1‖
SupportedinSQLServer2005andlaterversion
ALTERDatabase―test1‖ModifyName=―test‖
ANSWER
QUESTION 97

hirist
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WhatisaCursor?
99
QUESTION
AdatabaseCursorisacontrolwhichenablestraversalovertherowsorrecordsinthetable.Thiscanbeviewedasapointertoonerowinasetofrows.Cursorisverymuchusefulfortraversingsuchasretrieval,additionandremovalofdatabaserecords.
ANSWER
QUESTION 98

hirist
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WhatareMagicTablesinSQLServer?
100
QUESTION
InsertandDeletetablesarecreatedwhenthetriggerisfiredforanyDMLcommand.ThosetablesarecalledMagicTablesinSQLServer.Thesemagictablesareusedinsidethetriggersfordatatransaction.
ANSWER
QUESTION 99

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WhatisISNULL()operator?
101
QUESTION
ISNULLfunctionisusedtocheckwhethervaluegivenisNULLornotNULLinsqlserver.ThisfunctionalsoprovidestoreplaceavaluewiththeNULL.
ANSWER
QUESTION 100

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Resources
102
http://www.itechaleart.com/2013/05/top-50-sql-question-answers_11.html
https://www.katieandemil.com/sql-interview-questions-and- answers?tab=article#Question 4
http://www.dwbiconcepts.com/tutorial/24-interview-questions/190-top-20-sql- interview-questions-with-answers.html
http://a4academics.com/interview-questions/53-database-and-sql/411-sql- interview-questions-and-answers-database
http://narendra86.blogspot.com/2013/10/top-80-sql-query-interview- questions.html
http://crackaninterview.com/sql-queries-interview-questions-answers/
http://career.guru99.com/top-50-sql-question-answers/
http://www.indiabix.com/technical/sql-server-common-questions/
http://career.guru99.com/top-50-sql-server-questions-answers/
http://www.ittestpapers.com/sql-interview-questions(25-50).html
http://www.dotnetfunda.com/interviews/cat/8/sql-server
http://www.careerride.com/SQLServer-Interview-Questions.aspx

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