Muaj pes tsawg hom kev koom nrog hauv Oracle?
Muaj pes tsawg hom kev koom nrog hauv Oracle?

Video: Muaj pes tsawg hom kev koom nrog hauv Oracle?

Video: Muaj pes tsawg hom kev koom nrog hauv Oracle?
Video: Yog muaj 5 yam no ua pes tsawg lub hom phiaj los yeej tiav 2024, Kaum ib hlis
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4 hom sib txawv

Tsuas yog li ntawd, hom kev koom nrog yog dab tsi?

Muaj plaub qhov yooj yim hom ntawm SQL koom : sab hauv, sab laug, sab xis, thiab puv. Txoj kev yooj yim tshaj plaws thiab yooj yim tshaj plaws los piav qhia qhov txawv ntawm plaub qhov no hom yog los ntawm kev siv daim duab Venn, uas qhia tag nrho cov kev sib raug zoo ntawm cov ntaub ntawv teev.

Kuj Paub, (+) txhais li cas hauv SQL koom? Oracle sab nraud koom tus neeg ua haujlwm (+) tso cai rau koj ua yeeb yam sab nraud koom ntawm ob lossis ntau lub rooj. Piv txwv ceev: -- Xaiv tag nrho cov kab ntawm lub nroog cov lus txawm tias tsis muaj kab sib luag hauv cov nroog cov lus SELECT cov nroog.

Ib yam li ib tug yuav nug, dab tsi koom nrog hauv Oracle nrog piv txwv?

Oracle koom yog siv los ua ke kab los ntawm ob lossis ntau lub rooj raws li qhov tseem ceeb ntawm cov kab sib txuas. Cov kab ntawv cuam tshuam feem ntau yog thawj kab tseem ceeb ntawm thawj lub rooj thiab txawv teb chaws tseem ceeb ntawm lub rooj thib ob. Oracle txhawb sab hauv koom , sab laug koom , yog koom , puv sab nrauv koom thiab hla koom.

Dab tsi yog kev koom nrog sab laug hauv Oracle?

Taw qhia rau Oracle LEFT JOIN clause Yog tias ib khub kab ntawm ob lub rooj T1 thiab T2 txaus siab rau koom predicate, cov lus nug sib txuas cov kab ke ntawm cov kab hauv ob lub rooj thiab suav nrog cov kab no hauv qhov tshwm sim. Hauv lwm lo lus, a sab laug koom rov qab tag nrho cov kab los ntawm sab laug rooj thiab cov kab sib txuam los ntawm lub rooj sab xis.

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