Ifom yesithathu eqhelekileyo (3NF) ngumgaqo-siseko wemigaqo-siseko oxhasa ukuthembeka kwedatha ngokwakhiwa kwimigaqo yokuqhelanisa neenkcukacha ezibonelelwe ngeFom yoQeqesho oluQala (1NF) kunye neFomu yesiBini yesiQhelo (2NF).
Iimfuneko zeFom yeSithathu eziqhelekileyo
Kukho iimfuno ezimbini eziphambili kwi-database ukuba zibe kwifom yesithathu evamile:
- I-database kufuneka sele idibene neemfuno ze- 1NF kunye ne- 2NF .
- Zonke iikholomu zedata kufuneka zithembele kwiprayimari ebalulekileyo , nto leyo ithetha ukuba nayiphi na ixabiso lekholomu lingafumaneka kwi-key key kuphela.
Malunga nokuxhaswa kweSiseko esiPhambili
Makhe sihlolisise ngakumbi into esithetha ngayo kukuba zonke iikholamu zixhomekeke kwiyona nto ephambili.
Ukuba ixabiso lekholomu lingafumaneka kwizinto zombini eziphambili kwaye enye ikholomu etafileni, iphula i-3NF. Cinga ngetafile zabasebenzi ngeekholamu:
- EmployeeID
- Igama lokuqala
- Ifani
Ngaba i-LastName ne-FirstName ixhomekeke kuphela kwixabiso le-EmployeeID? Ewe, i-LastName ingaxhomekeka kwi-FirstName? Akunjalo, kuba akukho nto ivela kwi-LastName iza kubonisa inani leNkcazo yokuqala. Ngaba igama lokuqala lixhomekeka kwiNameName? Akukho kwakhona, ngokuba kunjalo into: nokuba yiyiphi i-LastName inokwenzeka, ayikwazi ukunika isicatshulwa njengexabiso leNkcazo yokuqala. Ngoko ke, le tafile i-3NF iyavumelana.
Kodwa qwalasela le tafile Iimoto:
- Imoto
- Umenzi
- Umzekelo
Umenzi kunye noMzekelo unokufumana kwi-VehicleID-kodwa uMzekelo unokufumana kwakhona kuMenzi-mveliso kuba imodeli yemoto yenziwa kuphela ngumenzi othile. Le tafile yelungiselelo ayiyiyo i-3NF ehambelanayo, kwaye ngoko ke ingakhokelela ekungcoleni kwedatha. Umzekelo, unokuhlaziya umenzi ngaphandle kokuhlaziya imodeli, ukufaka ukungalungi.
Ukuze senze okuhambelanayo, kufuneka sidlulise ikholomu ethe xhomekeke kwenye ityeyibhile kwaye siyibhekise ngokusebenzisa ikhiye yangaphandle. Oku kuya kubangela ietafile ezimbini:
Izithuthi zeThebula
Kwitheyibhile elingezantsi, i-ModelID yikhiye yangaphandle kwitafile zeModeli :
- Imoto
- Umenzi
- ModelID
Iimodeli zeThebula
Ezi modyuli zeemodeli ezintsha zeepalati kubenzi. Ukuba ufuna ukuhlaziya nayiphi na imoto yolwazi oluthile kumzekelo, uza kwenza kule tafile, kunokuba ubekwe kwitafile zeZithuthi.
- ModelID
- Umenzi
- Umzekelo
IiNdawo eziDeriweyo kwi-3NF Model
Itafile inokuthi iqulethe insimu efunyenweyo-enye ehlanganisiwe ngokusekelwe kwezinye iikholomu etafileni. Umzekelo, khawuqwalasele le tafile yee-widget oda:
- Inombolo yoku-oda
- Inombolo yomthengi
- Ixabiso lento
- Ubungakanani
- Iyonke
Ikhefu elipheleleyo lokuthotyelwa kwe-3NF kuba lingafunyanwa ngokuphindaphinda ixabiso leyunithi ngobungakanani, kunokuba luxhomekeke ngokupheleleyo kwi-key key. Simele sisuse kwitafile ukuthobela ifom yesithathu evamile.
Enyanisweni, ekubeni itholakala, kungcono ukuba ungayigcineli kwisiseko sedatha.
Siyakwazi ukuyiqhafaza "kwi-fly" xa wenza imibuzo egciniweyo. Ngokomzekelo, mhlawumbi sisetyenzisile le mbuzo ukufumana amanani omyalelo kunye nama totali:
UKUHLOLA iNomboloNombolo, Inani elivela kwi-WidgetOrdersNgoku sinokusebenzisa le mibuzo:
UKUHLOLA iNombolo, iNomboloI-UnitPrice * Ubungakanani BONKE I-AS KUNYE KWE-WidgetOrdersukufezekisa iziphumo ezifanayo ngaphandle kokuphula imithetho yokumisela.