Chechitatu chimiro chechimiro (3NF) inonyanya kushandisa nheyo yezvinyorwa inotsigira kuvimbika kwedhidziro kuburikidza nekuvaka pane zvinyorwa zvekuchengetedza mabhuku zvinopiwa neFirst Normal Form (1NF) uye yechipiri Fomu Yakafanana (2NF).
Yechipiri Yomufomu Yomufambi Yechidikanwa
Pane zvidimbu zviviri zvinodiwa kuti database ive yechitatu yefomu fomu:
- Dhiyabhorosi inofanira kunge yasati yasangana nezvinodiwa zvese 1NF ne 2NF .
- Zvose zvinyorwa zvepa database zvinofanira kuvimba nheyo yekutanga , zvinoreva kuti chero humwe hutori hunokosha hunogona kuwanikwa kubva pachigamba chekutanga.
Pamusoro peNheyo Nyanzvi yeKutenderera
Ngatitsvakei zvishoma nezvatinoreva kuburikidza nechokwadi chekuti mahwendefa ose anofanira kutarisana nekona yekutanga.
Kana nhamba yekorodhe inogona kutorwa kubva kune imwe chinhu chikuru uye imwe imwe column mutafura, inoputsa 3NF. Chimbofunga tafura yevashandi ine mapuranga awa:
- VashandiID
- Zita rokutanga
- Zita rokupedzisira
Itai zvose Zita Rokutanga uye Nhamba Yokutanga inongotarisa chete kukosha kweHakozi? Zvakanaka, kudarika Nhasi kunogona kuvimba neNotangiraName here? Aiwa, nokuti hapana chinhu chinowanikwa muNameName chingaratidza kukosha kweNokutangaName. Nhamba yekutanga ingagona kuvimba neNyoName? Kwete zvakare, nokuti zvakafanana ndezvechokwadi: chero chingave chine LastName, hachikwanise kupa ruzivo rwekukosha kwekutanga. Saka, tafura iyi 3NF inoenderana.
Asi funga nezveMotokari iyi tafura:
- VehicleID
- Manufacturer
- Muenzaniso
Muumbi uye Muenzaniso angatora kubva kuMotokari - asi Muenzaniso unogonawo kuwana kubva kuMugadziri nokuti motokari yemufananidzo inongowanikwa chete nemumwe muumbi. Iyi tafura yakagadzirwa isiri 3NF inogamuchirika, uye naizvozvo, inogona kukonzera kudarika kwemashoko. Semuenzaniso, iwe unokwanisa kugadzirisa mhizha pasina kuvandudza mufananidzo, kuisa zvisiri izvo.
Kuita kuti zvienderane, tinoda kuendesa humwe hutenderedzwa huripo kune imwe tafura uye tinotarisa iko uchishandisa kiyi yekunze. Izvi zvingaguma mumatafura maviri:
Motokari Indaneti
Mune tafura iri pasi apa, ModelID iri kiyi yekunze kune tafura yeModels :
- VehicleID
- Manufacturer
- ModelID
Models Table
Iyi itsva mapafura emagetsi mavara kune vanogadzira. Kana iwe uchida kuvandudza ruzivo rwemoto chero ipi zvayo kune imwe muenzaniso, iwe unogona kuzviita mutafura iyi, panzvimbo yeMotokari yemagetsi.
- ModelID
- Manufacturer
- Muenzaniso
Derived Fields muNNN Model
Tafura inogona kuva nemunda wakatorwa - imwe yakaverengwa kubva kune dzimwe mbiru dziri patafura. Somuenzaniso, funga tafura iyi yemaraji majeti:
- Order Number
- Nhamba yeKateresi
- Unit Price
- Kuwanda
- Total
Zvose zvinokonzera 3NF kutevedza nokuti zvinogona kuwanikwa nekuwedzera chikwata chechikwata nehuwandu, pane kuti zvive zvakazara zvizere nechokutanga chinokosha. Tinofanira kuibvisa kubva patafura kuti titeerere nechetomu fomu yechitatu.
Ichokwadi, sezvo yakabva, zviri nani kuti urege kuzvichengetedza mune dheseta zvachose.
Tinogona kungozvienzanisa "pamhepo" patinenge tichiita mibvunzo ye database. Somuenzaniso, tinogona kunge tashandisa mubvunzo uyu kutora nhamba dzehurumende nematendi:
Sarudza OrderNumber, Total FROM WidgetOrdersIye zvino tinogona kushandisa shanyo inotevera:
Sarudza OrderNumber, UnitPrice * Kuwanda AS Total FROM WidgetOrderskuti zvive nemigumisiro yakafanana kunze kwekutyora mitemo yekusimudzira.