Dab tsi yog cov cwj pwm hauv SQL?
Dab tsi yog cov cwj pwm hauv SQL?

Video: Dab tsi yog cov cwj pwm hauv SQL?

Video: Dab tsi yog cov cwj pwm hauv SQL?
Video: Data Science with Python! Analyzing File Types from Avro to Stata 2024, Kaum ib hlis
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Xav txog ib qho tus cwj pwm raws li acharacteristic

Lub database muaj cov ntxhuav, txhua tus uas muaj cov kab thiab kab. Txhua kab (hu ua tuple) yog cov ntaub ntawv teeb tsa uas siv rau ib yam khoom. Txhua kem muaj cov yam ntxwv uas piav txog cov kab; cov kab no yog cov yam ntxwv.

Kuj kom paub yog, dab tsi yog cov cwj pwm hauv database?

Feem ntau, ib tus cwj pwm yog tus yam ntxwv. Ib database Management System (DBMS), ib tus cwj pwm hais txog a database tivthaiv, xws li lub rooj. Nws kuj tseem yuav xa mus rau a database teb. Yam ntxwv piav qhia qhov xwm txheej hauv kab ntawm a database.

Tsis tas li ntawd, dab tsi yog qhov chaw thiab cov cwj pwm? Yam ntxwv uas txheeb xyuas tus neeg yuav suav nrog tej yam xws li tus lej social security lossis ib qho kev sib txuas ntawm cov tsiaj ntawv thiab cov lej uas cim tus neeg. Yam ntxwv uas piav cov koom haum hu ua non-key yam ntxwv . Yam ntxwv uas txheeb xyuas cov koom haum ( qhov chaw tus cim) hu ua tus yuam sij yam ntxwv.

Ib yam li ntawd, koj tuaj yeem nug, dab tsi yog tus cwj pwm?

Ib tus cwj pwm txhais tau tias yog ib tug zoo orcharacteristic ntawm ib tug neeg, qhov chaw, los yog yam. Lub neej tiag tiag thiab cov cim tsis tseeb muaj ntau yam yam ntxwv . Muaj qhov sib txawv ntawm yam ntxwv thiab qhov zoo, tab sis nws tsis yooj yim thiab qee tus yam ntxwv tuaj yeem suav tias yog ib qho tus cwj pwm los yog qhov zoo.

Dab tsi yog kev siv tus cwj pwm?

Feem ntau, ib tus cwj pwm yog tus yam ntxwv. InHTML, ib tus cwj pwm yog tus yam ntxwv ntawm nplooj ntawv, xws li font loj lossis xim. Yam ntxwv yog siv los amplify atg. Thaum lub Web browser txhais cov ntawv HTML, nws tseem yuav nrhiav nws yam ntxwv kom nws tuaj yeem tso saib cov nplooj ntawv Web site zoo.

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