Video: Dab tsi yog cov yam ntxwv tseem ceeb ntawm kev ua haujlwm nyob ruaj khov?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Kev ua haujlwm ntawm kev vam meej yog kev sib raug zoo uas muaj nyob nruab nrab ntawm ob yam ntxwv . Nws feem ntau muaj nyob nruab nrab ntawm tus yuam sij tseem ceeb thiab tsis yog tus cwj pwm tseem ceeb hauv ib lub rooj. Sab laug ntawm FD yog lub npe hu ua tus txiav txim siab, sab xis ntawm kev tsim khoom yog hu ua dependent.
Ntawm no, dab tsi yog cov yam ntxwv tseem ceeb ntawm kev ua haujlwm zoo?
Lub ntsiab yam ntxwv ntawm functional dependencies siv nyob rau hauv normalization: muaj ib tug-rau-ib kev sib raug zoo ntawm tus cwj pwm (s) nyob rau sab laug-tes (determinant) thiab cov nyob rau sab xis-tes ntawm ib tug functional dependency . Tuav rau txhua lub sijhawm.
Ib yam li ntawd, kev ua haujlwm nyob hauv DBMS yog dab tsi? Functional Dependency (FD) txiav txim siab txog kev sib raug zoo ntawm ib tus cwj pwm mus rau lwm tus cwj pwm hauv kev tswj hwm database ( DBMS ) system. Functional dependency pab koj tswj cov ntaub ntawv zoo hauv cov ntaub ntawv. Cov functional dependency X ntawm Y yog sawv cev los ntawm X → Y.
Hauv qhov no, dab tsi yog qhov ua haujlwm nyob ntawm?
A functional dependency (FD) yog kev sib raug zoo ntawm ob tus cwj pwm, feem ntau ntawm PK thiab lwm yam tsis tseem ceeb hauv ib lub rooj. Rau txhua qhov kev sib raug zoo R, tus cwj pwm Y yog functionally nyob ntawm tus cwj pwm X (feem ntau yog PK), yog tias rau txhua qhov siv tau ntawm X, tus nqi ntawm X tshwj xeeb txiav txim siab tus nqi ntawm Y.
Dab tsi yog qhov kev vam meej piav qhia nws nrog piv txwv?
Functional dependency hauv DBMS. Cov cwj pwm ntawm lub rooj tau hais tias yog nyob ntawm ib leeg thaum tus cwj pwm ntawm lub rooj tshwj xeeb txheeb xyuas lwm tus cwj pwm ntawm tib lub rooj. Rau piv txwv : Piv txwv tias peb muaj ib lub rooj tub ntxhais kawm nrog cov cwj pwm: Stu_Id, Stu_Name, Stu_Age.
Pom zoo:
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