Normalizing koj Database
Yog hais tias koj tau ua hauj lwm nrog databases rau ib ntus, yuav muaj feem cuam koj tau hnov lub sij hawm normalization. Tej zaum ib tug neeg tau nug koj tias "Yog tias cov ntaub ntawv teev ntaub ntawv?" los yog "Puas yog nyob rau hauv BCNF ?" Feem ntau yog khov dua ua ib qho khoom plig uas tsuas yog kawm tau sijhawm xwb. Txawm li cas los, kev paub txog cov qauv ntawm kev ua haujlwm thiab thov kev pabcuam rau koj tus qauv database txhua hnub tiag tiag tsis yog txhua yam uas nyuaj thiab nws yuav ua kom zoo dua ntawm koj qhov DBMS.
Nyob rau hauv tsab xov xwm no, peb yuav ua kom paub txog lub tswv yim ntawm kev ua haujlwm thiab sau me ntsis cov ntaub ntawv zoo tshaj plaws.
Qhov Kev Ntsuas Yog Dab Tsi?
Kev ua lag luam yog qhov txheej txheem ntawm kev sib koom tes nrhiav cov ntaub ntawv hauv cov ntaub ntawv. Muaj ob lub hom phiaj ntawm cov txheej txheem ntawm kev ua haujlwm: tshem tawm cov ntaub ntawv rov qab (piv txwv, khaws cia tib cov ntaub ntawv hauv ntau dua ib lub rooj) thiab kom ntseeg tau tias cov ntaub ntawv txuas tau zoo (tsuas khaws cov ntaub ntawv hauv cov rooj ntawv). Ob qho no yog lub hom phiaj tsim nyog los ntawm lawv txo qhov nyiaj ntawm qhov chaw siv lub database siv thiab xyuas kom meej tias cov ntaub ntawv yog qhov muab khaws cia.
Cov Ntawv Ceev
Lub zej zog database tau tsim ib co txheej txheem rau kev ua kom ntseeg tau tias cov databases yog kev ua haujlwm. Cov no raug xa mus ua cov ntaub ntawv zoo li qub thiab raug suav los ntawm ib qho (qhov qis tshaj ntawm kev hloov cev, hu ua thawj daim qauv lossis 1NF) txog tsib (tsib daim ntawv thib 5 lossis 5NF). Hauv cov ntawv siv, koj yuav pom ntau zaus 1NF, 2NF, thiab 3NF nrog rau 4NF. Tsib tsib daim ntawv no tsis tshua muaj pom thiab yuav tsis tham txog hauv tsab xov xwm no.
Ua ntej peb pib sib tham txog cov ntaub ntawv li qub, nws tseem ceeb uas taw qhia tias lawv yog cov txheej txheem thiab cov txheej txheem xwb. Qee zaus, nws yuav tsim nyog los tawm tsam lawv kom ua raws li kev lag luam kev ua haujlwm. Txawm li cas los xij, thaum hloov qhov chaw txawv, nws tseem ceeb heev rau kev soj ntsuam txhua yam kev tau txais kev puas tsuaj uas lawv muaj nyob rau hauv koj lub tshuab thiab suav nyiaj rau kev tsim kev tsis sib haum xeeb. Hais tias, peb tau tshawb txog cov ntaub ntawv li qub.
Thawj Daim Ntawv Xub Thawj (1NF)
Thawj daim ntawv (1NF) teev cov cai tswjfwm txog kev tsim kho rau cov ntaub ntawv:
- Tshem tawm txhua yam ntawm tib lub rooj.
- Tsim cov lus sib cais rau txhua pawg ntawm cov ntaub ntawv muaj feem xyuam thiab txheeb xyuas txhua kab nrog ib kem lossis kab ntawm kab ( thawj qhov tseem ceeb ).
Daim Ntawv Teev Npe Thib Ob (2NF)
Ob daim ntawv thib ob (2NF) ntxiv rau lub tswv yim ntawm kev tshem cov ntaub ntawv khaws cia :
- Ntsib tag nrho cov kev cai ntawm daim ntawv xub thawj.
- Tshem cov lej ntawm cov ntaub ntawv uas siv rau ntau kab ntawm ib lub rooj thiab muab lawv tso rau hauv cov lus cais.
- Tsim kev sib raug zoo ntawm cov tshiab cov ntxhuav thiab lawv cov neeg ua ntej los ntawm kev siv cov yuam sij txawv teb chaws .
Daim Ntawv Teev Npe Thib Peb (3NF)
Daim npav thib peb (3NF) mus rau ib qho loj loj ntxiv:
- Ntsib tag nrho cov kev cai ntawm daim ntawv thib ob.
- Tshem txhua kab uas tsis nyob ntawm thawj qhov tseem ceeb.
Boyce-Codd Daim Ntawv Teev Tseg (BCNF los yog 3.5NF)
Daim Ntawv Teev Daim Ntawv Teev Tseg, uas yog hu ua "thib peb thiab ib nrab (3.5)", ntxiv rau ib qho ntxiv:
- Ntsib tas nrho cov cai ntawm peb daim ntawv thib peb.
- Txhua qhov kev txiav txim siab yuav tsum yog tus neeg sib tw qhov tseem ceeb.
Daim Ntawv Xaj Ntawm 4 (4NF)
Thaum kawg, daim npav thib plaub (4NF) muaj ib qho kev xav tau ntxiv:
- Ntsib tas nrho cov cai ntawm peb daim ntawv thib peb.
- Ib qho kev sib raug zoo yog nyob rau hauv 4NF yog tias nws tsis muaj kev vam khom nqi .
Nco ntsoov, cov txheej txheem kev coj ua niaj hnub no yog qhov zoo. Rau ib tug database yuav tsum nyob rau hauv 2NF, nws yuav tsum xub ua tiav tag nrho cov txheej xwm ntawm ib cov database 1NF.
Kuv yuav tsum tau ua kom cev?
Thaum database normalization feem ntau yog ib lub tswv yim zoo, nws tsis yog qhov yuav tsum tau ua kom tiav. Qhov tseeb, muaj qee qhov uas ua txhob txwm ua txhaum txoj cai ntawm kev ua txhaum yog qhov zoo. Yog xav paub ntxiv txog nqe lus no, nyeem Kuv Yuav Tsum Tau Kho Kuv Database?
Yog tias koj xav kom koj database zoo li qub, pib nrog kev kawm tso koj cov ntaub ntawv rau hauv Thawj Daim Ntawv .