Peb puas tuaj yeem siv tsis muaj pab pawg los ntawm Oracle?
Peb puas tuaj yeem siv tsis muaj pab pawg los ntawm Oracle?

Video: Peb puas tuaj yeem siv tsis muaj pab pawg los ntawm Oracle?

Video: Peb puas tuaj yeem siv tsis muaj pab pawg los ntawm Oracle?
Video: Hais Uas Lus Hmoob: Quantitative Adjectives Part 1 2024, Kaum ib hlis
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Taw qhia rau lub Oracle HAV lus

Nws yog siv lim pab pawg ntawm kab rov qab los ntawm PIB YOG clause. Yog koj siv tus MUAJ lus tsis muaj tus PIB Los ntawm clause, lub MUAJ clause ua haujlwm zoo li WHERE clause. Nco ntsoov tias cov MUAJ clause cov ntxaij lim dej pab pawg ntawm kab thaum qhov WHERE clause lim kab.

Ib yam li ntawd, peb puas tuaj yeem siv suav tsis suav nrog?

Peb yog kuj tau siv windowing muaj nuj nqi nrog lub COUNT ua hauj lwm nyob rau hauv ib tug xaiv nqe lus li ntawd peb tuaj yeem siv suav hauv SQL tsis muaj xav tau ib pab pawg ntawm clause. Cov lus xaiv saum toj no yuav tau kawg ua tsis tau li peb tsis tau suav nrog a pab pawg los ntawm thiab cov COUNT muaj nuj nqi yog ib tug aggregate muaj nuj nqi.

Ib yam li ntawd, puas xav tau pab pawg los ntawm? xaiv 1 muaj 1 = 1; Yog li muaj tsis yog xav tau pab pawg los ntawm . Muaj yog thov tom qab lub aggregation theem thiab yuav tsum tau siv yog tias koj xav lim aggregate tau. Hauv cov ntsiab lus, muaj yog thov tom qab lub pab pawg los ntawm theem whereas qhov twg yog thov ua ntej lub pab pawg los ntawm theem.

Ib yam li ntawd, koj tuaj yeem siv pab pawg los ntawm yam tsis muaj kev sib sau?

Koj siv tau tus PIB YOG clause tsis muaj thov ib tag nrho muaj nuj nqi. Cov lus nug hauv qab no tau txais cov ntaub ntawv los ntawm lub rooj them nyiaj thiab pab pawg qhov tshwm sim los ntawm tus neeg siv khoom id. Hauv qhov no, lub PIB Los ntawm kev ua haujlwm zoo li DISTINCT clause uas tshem tawm cov kab sib npaug ntawm qhov tshwm sim.

Peb puas tuaj yeem siv muaj clause ua ntej pawg los ntawm?

Cov ntsiab lus. Cov PIB YOG Clause yog siv rau pab pawg kab uas muaj nqi tib yam. Daim ntawv SELECT siv hauv PIB YOG clause tau tsuas yog ua siv muaj cov npe kab, cov haujlwm sib sau ua ke, qhov tsis tu ncua thiab cov kab lus. Cov HNUB NO yog siv txwv tsis pub cov txiaj ntsig rov qab los ntawm cov PIB YOG lus.

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