Basa rakakwana rinoshandiswa kune imwe nzvimbo yepamusoro-soro yepamutemo inofananidzwa nehuwandu hwemaitiro eChipiri Chechimiro Chechipiri (2NF) . Muchidimbu, izvi zvinoreva kuti inosangana nezvinodiwa zveTrans Normal Form (1NF), uye zvisizvo zvisiri izvo zvinokosha zvinoshanda zvakakwana zvichienderana nekona yekutanga.
Izvi hazvisi zvakaoma sezvazvinogona kurira. Ngatitarisei pane izvi zvakajeka.
Nhepfenyuro yeFomu Yokutanga Yakarongeka
Pamberi pebhuku rinogona kunyatsogadzikana, rinofanira kutanga ritenderana neFirst Normal Form .
Zvose izvi zvinoreva kuti nhengo imwe neimwe inofanirwa kubata chinhu chimwechete, atomiki.
Somuenzaniso, tafura inotevera haifaniri kutevedzera 1NF, nokuti mushandi Tina akabatanidzwa kune nzvimbo mbiri, zvose zviri muchitokisi chimwe chete:
Mushandi | Nzvimbo |
---|---|
John | Los Angeles |
Tina | Los Angeles, Chicago |
Kubvumira izvi zvigadzirwa zvinogona kukanganisa kushandiswa kwemashoko kana zvinyorwa. Kuti uone 1NF kutevedza, gadzirisa tafura kuitira kuti zvese (kana kuti makoromeri masero) aite chinhu chimwe chete:
Mushandi | Nzvimbo |
---|---|
John | Los Angeles |
Tina | Los Angeles |
Tina | Chicago |
Asi 1NF haisati yakwana kudzivisa zvinetso nedata.
Nzira 2NF Inoshanda Sei Kuti Uve Nechokwadi Chekudzivirira
Kuti zvive zvizere zvakakwana, zvose zvisati zvichisarudzwa zvinokosha zvinofanirwa zvichienderana nekona yekutanga. (Yeuka, chinhu chinonyanya kukosha chiri chinhu chinokosha (somuenzaniso, chinhu chikuru kana chekunze) chinoshandiswa kunyanya kuziva rekodhi rekodhi.
Vashandi vekugadzira mapepa vanoshandisa rukuro kurondedzera hukama huripo huri pakati pezvinhu:
Kana chirevo A chichisarudzira kukosha kweB, tinonyora izvi A -> B - zvinoreva kuti B inoshanda zvichienderana neA A. Muukama uhwu, A inotarisa kukosha kweB, apo B iripo A.
Semuenzaniso, mune iri rekushanda kwemashandisirwo emabasa, EmployeeID neDeptID ndevamwe vheti dzekugadzirira: Bhizimisi ndiro ndiro gwaro rekutanga apo DeptID iri chinyorwa chekunze.
Chero humwe humwe unhu - munyaya iyi, EmployeeName uye DeptName - inofanira kuvimba nekona yekutanga yekuwana kukosha kwayo.
VashandiID | EmployeeName | DeptID | DeptName |
---|---|---|---|
Emp1 | John | Dept001 | Mari |
Emp2 | Tina | Dept003 | Sales |
Emp3 | Carlos | Dept001 | Mari |
Muchiitiko ichi, tafura haina kunyanya kuvimba nokuti, nepo EmployeeName inofanana nechokutanga chinoita Bashandi, iDepName inofanirwa panzvimbo yeDeptID. Izvi zvinonzi kusarura zvishoma .
Kuti ita tafura iyi ienderane ne 2NF, tinoda kuparadzanisa data mumatafura maviri:
VashandiID | EmployeeName | DeptID |
---|---|---|
Emp1 | John | Dept001 |
Emp2 | Tina | Dept003 |
Emp3 | Carlos | Dept001 |
Tinobvisa chimiro cheDeptName kubva patafura yeVashandi uye tinogadzira mapurisa matsva mapoka:
DeptID | DeptName |
---|---|
Dept001 | Mari |
Dept002 | Human Resources |
Dept003 | Sales |
Iye zvino hukama huri pakati pematafura hunozara zvakakwana, kana mu 2NF.
Chikonzero nei Kunyatsovimbika Kunokosha
Kunyatso kutarisa pakati pezvigadzirwa zvemashoko kunobatsira kuvimbisa kuderera kwe data uye kudzivisa kudarika kwezvinhu.
Semuenzaniso, funga tafura iri muchikamu chiri pamusoro apa inoteerera 1NF chete. Heino iyo, zvakare:
Mushandi | Nzvimbo |
---|---|
John | Los Angeles |
Tina | Los Angeles |
Tina | Chicago |
Tina ane mbiri zvinyorwa. Kana tikadzokorora mumwe tisingazivi kuti pane maviri, chigumisiro chacho chingave chisingabvumirwi.
Kana, zvakadini kana tichida kuwedzera mushandi patafura ino, asi isu tisati taziva Nzvimbo? Tingave tisingabvumirwi kunyange kuwedzera mushandi mutsva kana nzvimbo yemoyo isingabvumi NULL maitiro.
Kuzara zvakakwana hausi mufananidzo wose, kunyange zvakadaro, kana zvasvika pakushambadzira. Iwe unofanirwa kuve nechokwadi chekuti database yako iri muTatu Normal Form (3NF).