Esikhathini esincane esisebenzayo sokuxhomekeka kokusebenza okuyisici kukhona i-subset yenye
Ezweni lezintandokazi zesisekelo sedatha, ukuxhomekeka okusebenzayo kukhona uma isici esisodwa sinquma esinye isici ku-database. Ukuthembela okuncane okusebenzayo kuyinkinga yokuxhomekeka kwedatha eyenzekayo lapho ichaza ukuxhomekeka kokusebenza kwesici noma iqoqo lezimfanelo ezifaka imfanelo yokuqala.
Izibonelo Zokuthembela Okungasebenzi Okungavamile
Lolu hlobo lokuthembela lubizwa ngokuthi luyinto encane ngoba lungatholakala ekuhlakanipheni. Uma "ohlangothini" olulodwa luyisigatshana somunye, kuthathwa njengento encane. Uhlangothi lwesobunxele lubhekwa njengento enqunyiwe futhi ilungile othembekile .
- {A, B} -> B iyinto encike ekusebenzeni ngokweqile ngoba iB isigaba se- A, B. Njengoba i- { A, B} -> B ihlanganisa B , inani le- B linganqunywa. Kuyinto encike ekusebenzeni ngokweqile ngoba ukunquma B kunelisekile ngobuhlobo bayo no-A, B. Njengoba amanani ka- B anqunywa ngamanani we- A , noma yikuphi okulandelanayo okwabelwana ngezindinganiso ze- A kuzoba namanani afanayo okufanayo no- B . Enye indlela yokubeka ukuthi yonke i- B ifakiwe ku- A , yingakho kungaphansi kwe- A .
- {Employee_ID, Employee_Name} -> Employee_ID iphinde incike ekusebenzeni kusukela ku- Employee_ID kuyisigatshana se- {Employee_ID, Employee_Name} .
- Kuyafana no- A -> A noma u- Employee_ID -> Employee_ID, no- Employee_Name -> Employee_Name . Lezi zonke izixhomeke zokusebenza ezincane.
- Uma ukuxhomekeka okusebenzayo kwe-X-> Y, no-Y kuyi-subset ye-X, lokhu kuyinto encike ekusebenzeni okuncane. Uma i-Y engeyona i-subset ye-X, lokhu akuyona into encike ekusebenzeni.