面试时最经常被问到的问题（Frenquentlyaskedinterviewquestions）之Databases篇

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DatabasesQuestions&Answers

1.     WhataretwomethodsofretrievingSQL?
Answer:

2.     Whatcursortypedoyouusetoretrievemultiplerecordsets?
Answer:

3.     Whatactiondoyouhavetoperformbeforeretrievingdatafromthenextresultsetofastoredprocedure?
Answer:Movethecursordownonerowfromitscurrentposition.AResultSetcursorisinitiallypositionedbeforethefirstrow.Beforeyoucangettothefirstrow,youwouldneedtoMovethecursordownbyonerow(Forex:injavathefirstcalltonextmakesthefirstrowthecurrentrow;thesecondcallmakesthesecondrowthecurrentrow,andsoon).

4.     WhatisthebasicformofaSQLstatementtoreaddataoutofatable?
Answer:SELECT*FROMtable_name;

5.     Whatstructurecanyouhavethedatabasemaketospeeduptablereads?
Answer:Thequestionisnotcorrect."Whatstructurecanyouhavethedatabasemaketospeeduptablereads?"Itisnotclearwhatexactlytheterm"structure"meansinthiscase.FollowtherulesofDBtuningwehaveto:
1)properlyuseindexes(differenttypesofindexes)
2)properlylocatedifferentDBobjectsacrossdifferenttablespaces,filesandsoon.
3)Createaspecialspace(tablespace)tolocatesomeofthedatawithspecialdatatypes(forexampleCLOB,LOBand...)
4)...
5)...

6.     Whatisa"join"?
Answer:Joinsmergethedataoftworelatedtablesintoasingleresultset,presentingadenormalizedviewofthedata.

7.     Whatisa"constraint"?
Answer:Aconstraintallowsyoutoapplysimplereferentialintegritycheckstoatable.Thereare5primarytypesofconstraintsthatarecurrentlysupportedby:
PRIMARY/UNIQUE-enforcesuniquenessofaparticulartablecolumn.
DEFAULT-specifiesadefaultvalueforacolumnincaseaninsertoperationdoesnotprovideone.
FOREIGNKEY-validatesthateveryvalueinacolumnexistsinacolumnofanothertable.
CHECK-checksthateveryvaluestoredinacolumnisinsomespecifiedlist
NOTNULL-isaconstraintwhichdoesnotallowvaluesinthespecificcolumntobenull.Andalsoitistheonlyconstraintwhichisnotatablelevelconstraint.

8.     Whatisa"primarykey"?
Answer:PrimaryKeyisatypeofaconstraintenforcinguniquenessanddataintegrityforeachrowofatable.AllcolumnsparticipatinginaprimarykeyconstraintmustpossesstheNOTNULLproperty.

9.     Whatisa"functionaldependency"?Howdoesitrelatetodatabasetabledesign?
Answer:Whatfunctionaldependenceinthecontextofadatabasemeansisthat:AssumethatatableexistsinthedatabasecalledTABLEwithacompositeprimarykey(A,B)andothernon-keyattributes(C,D,E).Functionaldependencyingeneral,wouldmeanthatanynon-keyattribute-CDorEbeingdependentontheprimarykey(AandB)inourtablehere.1<script type="text/javascript"><!--google_ad_client = "pub-2947489232296736";/* 728x15, 创建于 08-4-23MSDN */google_ad_slot = "3624277373";google_ad_width = 728;google_ad_height = 15;//--></script><script type="text/javascript"src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script>

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