Ib lub ntsiab lus uas siv hauv database tsim yog ib qho "kev sib txuas lus database" -tab sis ib qho kev sib txuas database tsis yog tib yam thiab tsis tau hais, raws li nws lub npe pom, muaj kev sib raug zoo ntawm cov ntxhuav. Tiam sis, ib qho kev sib txuas lus tsuas hais txog ib tus neeg hauv lub rooj nyob hauv cov ntaub ntawv keeb kwm.
Hauv cov ntaub ntawv sib piv , cov lus no yog qhov sib piv vim tias nws khaws cov kev sib raug zoo ntawm cov ntaub ntawv hauv nws txoj kab-kab. Cov kab yog cov lus ntawm cov lus, thaum cov kab sawv cev cov ntaub ntawv khaws tseg. Ib tug kab nkaus xwb yog hu ua tuple rau database designers.
Lub ntsiab lus thiab cov khoom ntawm kev sib raug zoo
Ib tug piv, los yog cov lus, nyob rau hauv ib qho kev sib txuas ntawm cov ntaub ntawv muaj tej yam khoom. Ua ntej tshaj tawm, nws lub npe yuav tsum yog tus cim nyob rau hauv database, piv txwv li cov ntaub ntawv database tsis muaj ntau lub rooj ntawm tib lub npe. Tom ntej no, txhua qhov kev sib txuas yuav tsum muaj ib qho ntawm cov kab, los yog cov cwj pwm, thiab nws yuav tsum muaj ib co txheej txheem kom muaj cov ntaub ntawv. Xws li cov lus lub npe, tsis muaj cov cwj pwm yuav muaj tib lub npe.
Tom ntej no, tsis muaj tuple (los yog kab) ua ib tug duplicate. Hauv kev xyaum, cov ntaub ntawv tej zaum yuav muaj cov kab sib txuas, tab sis nws yuav tsum muaj kev coj ua nyob hauv qhov chaw kom tsis txhob muaj qhov no, xws li kev siv cov thawj lub npe yuam (ntxiv mus).
Muab hais tias tus tuple yuav tsis ua ib tug duplicate, nws ua raws li qhov sib txhawv yuav tsum muaj tsawg kawg yog ib tus attribute (los yog kem) uas qhia txhua tuple (los yog kab) uniquely. Qhov no yog qhov tseem ceeb. Cov thawj qhov tseem ceeb no tsis tuaj yeem hloov tau. Qhov no txhais tau tias tsis muaj tuple tuaj yeem muaj tib lub cim, thawj qhov tseem ceeb. Tus yuam sij tsis tuaj yeem muaj tus nqi NULL , uas tsuas txhais tau hais tias tus nqi yuav tsum paub.
Tsis tas li ntawd, txhua lub cell, los yog teb, yuav tsum muaj ib qho nqi. Piv txwv li, koj nkag tsis tau ib yam dab tsi zoo li "Tom Smith" thiab cia siab tias lub database nkag siab tias koj muaj lub npe thiab lub xeem; theej, tus database yuav to taub tias tus nqi ntawm cov xovtooj ntawm no yog raws nraim li cas tau nkag.
Thaum kawg, tag nrho cov cwj pwm-los yog kab-yuav tsum yog tib lub npe, txhais tau hais tias lawv yuav tsum muaj tib hom ntaub ntawv. Koj tsis tuaj yeem sib tov ib txoj hlua thiab tus lej hauv ib zaug xwb.
Tag nrho cov khoom no, los yog kev txwv, ua kom ntseeg tau tias muaj kev ruaj ntseg ntawm cov ntaub ntawv, tseem ceeb heev kom muaj tseeb ntawm cov ntaub ntawv.