Yuav tsum yog tus yuam sij tseem ceeb yog qhov tshwj xeeb?

Cov txheej txheem:

Yuav tsum yog tus yuam sij tseem ceeb yog qhov tshwj xeeb?
Yuav tsum yog tus yuam sij tseem ceeb yog qhov tshwj xeeb?

Video: Yuav tsum yog tus yuam sij tseem ceeb yog qhov tshwj xeeb?

Video: Yuav tsum yog tus yuam sij tseem ceeb yog qhov tshwj xeeb?
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Anonim

Tus yuam sij tseem ceeb yuav tsum yog qhov tshwj xeeb. Tus yuam sij tshwj xeeb tsis tas yuav yog tus yuam sij tseem ceeb - saib tus neeg sib tw tus yuam sij. Qhov ntawd yog, tej zaum yuav muaj ntau tshaj ib qho kev sib txuas ntawm kab ntawm ib lub rooj uas tuaj yeem txheeb xyuas ib kab - tsuas yog ib qho ntawm cov no tuaj yeem xaiv los ua tus yuam sij tseem ceeb.

Yuav ua li cas yog tus yuam sij tseem ceeb tsis txawv?

Txawm tias thaum lub ntsiab_key tau txhais nyob rau hauv txhua qhov kev pom (thiab txhua qhov yog qhov tseeb tshwj xeeb), koj tuaj yeem pom qhov tsis muaj nqi tshwj xeeb / qhov yuam kev tseem ceeb thaum khiav cov lus nug. Qhov no tuaj yeem tshwm sim thaum muaj ntau yam one_to_many koom nrog hauv Kev Tshawb Fawb thiab muaj qhov ntsuas uas sib sau ua ke ntawm cov txiaj ntsig los ntawm ob lossis ntau lub rooj sib txawv

Vim li cas tag nrho cov ntsiab lus tseem ceeb yuav tsum yog qhov tshwj xeeb?

Primary key ncig kev ncaj ncees rau lub rooj. … Ib lub rooj tuaj yeem muaj ntau dua ib tus yuam sij tshwj xeeb tsis zoo li tus yuam sij tseem ceeb. Cov kev txwv tseem ceeb tshwj xeeb tuaj yeem lees txais tsuas yog ib qho NULL tus nqi rau kab. Cov kev txwv tshwj xeeb kuj tau hais los ntawm tus yuam sij txawv teb chaws ntawm lwm lub rooj.

Puas yog tus yuam sij tseem ceeb yuav tsum muaj qhov tshwj xeeb?

A tus yuam sij tseem ceeb yuav tsum yog tus cim. Tus yuam sij tshwj xeeb tsis tas yuav yog tus yuam sij tseem ceeb - saib tus neeg sib tw tus yuam sij. Qhov ntawd yog, tej zaum yuav muaj ntau tshaj ib qho kev sib txuas ntawm kab ntawm ib lub rooj uas tuaj yeem txheeb xyuas ib kab - tsuas yog ib qho ntawm cov no tuaj yeem xaiv los ua tus yuam sij tseem ceeb.

Puas yog tus yuam sij tseem ceeb tsis yog qhov txawv?

Cov yuam sij tseem ceeb tsis tas yuav tshwj xeeb los ntawm kev txhais (txawm tias lawv nyob hauv MySQL). Muaj cov txheej txheem database uas tso cai rau "cov yuam sij tsis tseem ceeb", vim tias lawv tswj hwm lawv tus kheej, feem ntau muab zais, "primary key" hauv "Low ID ".

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