Raw data



Definition

Inthedatabase:Rawdata,alsoknownasuserdata,isdatathathasnotbeenprocessedorsimplified.Thesedatamayormaynotbeinmachine-readableform.Itconstitutesdatathatphysicallyexists.Generallythereareseveralbasicdatatypesinthedatabase.

Metadata

Metadataisthedatainthesystemdatabase,anditsmainbodyisthedatadictionary.Thedatadictionaryisacollectionofvariousdescriptioninformationandcontrolinformationinthedatabasesystem.Metadataisusedtodescribethecharacteristicsofotherdataandprovidebackgroundinformationandmeaningdata.Generally,metadataisalsousedtodescribethedatastructure,dataelements,internalrelationshipsandothercharacteristicsofthedata.Italsoallowsdatatobetracedtotheindividualwhogeneratedthedata.Thepurposeofitsuseistoidentifyresources;evaluateresources;trackchangesintheuseofresources;realizesimpleandefficientmanagementoflargeamountsofnetworkeddata;realizeeffectivediscovery,search,integratedorganizationofinformationresources,andeffectivemanagementofusedresources.

Basictype

Charactertype

char[(length)]fixed-lengthcharacterupto2000bytes

varchar2[(length)]Variable-lengthcharacterdatatype,upto4000bytes

NCHAR[(length)]Fixed-lengthcharacterdatatype,composedofcharactersfromtheNationalLanguageSupport(NLS)characterset,Upto2000bytes

LONGvariable-lengthcharacterdatatypeupto2GB

RAWrawbinarydatatypeupto2000bytes

longrawprimitivebinarydatatype,thelongestis2GB

A12-byteaddressintherawdatabase,usedtolocatearowonthediskandtheobjectitpointsto

urawidgeneralTherawid,usedinthetable,isarepresentationoftherowprimarykey

largeobject

bloblargeprimitivebinaryobject,themaximumlengthis4GB

cloblargecharacterobject,Themaximumlengthis4GB

nclobThelargecharacterdatacomposedofNLScharactersetcharacters,themaximumlengthis4GB

bfileprovidessupportforoperatingsystemBinaryfileaccessinthefile,maximum4GB

Datetype

dateA7-bytedate/timedatatypewithfixedwidth,including7attributes:century,year,Month,day,hour,minute,second

timestamp7-byteor12-bytefixed-widthdate/timedatatype,whichcancontaindecimalsecondswhenitisdifferentfromDATE,andthedecimalpointcanretainupto9digits

timestampwithtimezornprovidessupportfortimezone

timestampwithlocaltimezornisatimezonesensitivetimetype

interalyeartomonthstorageoftheyearandmonth,canbeAddandsubtractdateandtimestamptypes

intervaldaytosecondstoresdays/hours/minutes/seconds,andsupports9decimalseconds

datatype

number[(precision[,scale])]Range1~38

Thenumberofdigitsintheprecisionnumber

Thenumberofdigitstotherightofthedecimalpoint

/p>

oralceonlyprovidesonenumbertype:NUMBERtype,storedinoracleMostofthestoreddigitaldatacanberegardedasnumbertype(supportbinary_float,binary_doubleafter10g).ThefollowingdatatypesarecompatiblewithANSISQL:

/**

ANSISQL:AmericanNationalStandardsInstitute(ANSI)"isanorganizationthatapprovesmultipleindustrystandards.SQLasarelationshipThestandardlanguageusedbythetypedatabasewasoriginallyapprovedin1986basedontheimplementationofIBM.In1987,the"InternationalOrganizationforStandardization(ISO)"adoptedANSISQLasaninternationalstandard.Thisstandardwasrevisedin1992(SQL-92),revisedagainin1999(SQL-99).ThelatestoneisSQL-2003.

**/

float

numberic

decimal

number

integer

int

smallint

doubleprecision

real

Researchdirection

Thequalityoftheoriginaldatahasagreatrelationshipwiththelaterdatareadingandprocessing.NowtheresearchontheoriginaldataMainlyintermsofdataacquisitionanddatacompression,manymethodshavebeenproposedinthisregard.Forexample,theSARoriginaldatacompressionalgorithmbasedonliftingwaveletbelongstotransformcoding.Unlikedirectcodingmethods,transformcodingfirsttransformstheoriginaldataandthenQuantizationcodingtransformcoefficients.Thepurposeoftransformistomapthespatialdomainpixelarrayintoanuncorrelatedandcompactenergydistributiontransformcoefficientarray.Atthistime,thelargetransformcoefficientsthataccountfortheminorityrepresentthemostimportantenergycomponentsoftheimage,andthemajorityareThesmalltransformcoefficientsrepresentsomeunimportantdetailcomponents.Thedetailcomponentsrepresentedbythesmallcoefficientsareremovedbyquantization,andasmallamountofcodewordsareusedtodescribethemainenergyrepresentedbythelargecoefficientstoachieveahighcompressionratio.

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