Video: Pab pawg tuaj yeem siv yam tsis muaj?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Siv muaj tsis muaj pab pawg los ntawm. Cov lus nug nrog a muaj clause kuj yuav tsum muaj a pab pawg ntawm clause. Yog koj omit pab pawg los ntawm, tag nrho cov kab tsis cais los ntawm qhov twg clause rov qab los ua ib leeg pab pawg . Vim tsis muaj kev sib koom ua ke ntawm qhov twg thiab muaj clauses, lawv tsis tuaj yeem ua tus kheej ntawm ib leeg.
Tsis tas li, pab pawg tuaj yeem siv yam tsis muaj kev sib sau ua ke?
Koj siv tau tus PIB YOG clause tsis muaj thov ib aggregate muaj nuj nqi . Cov lus nug nram 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.
Tsis tas li ntawd, qhov sib txawv ntawm pawg los ntawm thiab muaj li cas? Lub ntsiab qhov sib txawv ntawm THAUM thiab MUAJ clause los thaum siv ua ke nrog PIB Los ntawm clause, Nyob rau hauv rooj plaub ntawd qhov twg yog siv los lim kab ua ntej pab pawg thiab MUAJ yog siv los tshem tawm cov ntaub ntawv tom qab pab pawg . Koj tuaj yeem siv WHERE clause yam tsis muaj MUAJ los yog PIB YOG, raws li koj tau pom ntau zaus.
Tom qab ntawd, lo lus nug yog, 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.
Peb puas tuaj yeem siv muaj clause yam tsis muaj kab lus nyob qhov twg?
Taw qhia rau Oracle HNUB NTAWD Nws yog siv txhawm rau lim pab pawg ntawm kab rov qab los ntawm GROUP BY lus . Yog koj siv tus TSIS MUAJ clause tsis muaj lub GROUP BY lus , cov HNUB NO ua haujlwm zoo li qhov chaw lus . Nco ntsoov tias cov HNUB NO lim pab pawg ntawm kab thaum nyob qhov twg lus lim kab.
Pom zoo:
Koj puas tuaj yeem siv pab pawg tsis muaj kev sib sau?
Koj tuaj yeem siv GROUP BY clause yam tsis tas siv cov haujlwm sib sau ua ke. Cov lus nug nram qab no tau txais cov ntaub ntawv los ntawm lub rooj them nyiaj thiab pab pawg cov txiaj ntsig los ntawm tus neeg siv khoom id. Hauv qhov no, GROUP BY ua haujlwm zoo li DISTINCT clause uas tshem tawm cov kab sib npaug ntawm qhov tshwm sim
Ib qho chaw tsis muaj zog puas tuaj yeem muaj qhov chaw tsis muaj zog?
Hom chaw tsis muaj zog muaj qee qhov yuam sij. Nco tseg- Lub koom haum tsis muaj zog ib txwm muaj kev koom tes tag nrho tab sis lub koomhaum muaj zog yuav tsis muaj tag nrho kev koom tes.Weak entity yog nyob ntawm qhov chaw muaj zog kom ntseeg tau tias muaj qhov tsis muaj zog. Zoo li lub koom haum muaj zog, qhov tsis muaj zog tsis muaj qhov tseem ceeb, Nws muaj feem cuam tshuam kev ntxub ntxaug
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Peb puas tuaj yeem siv tsis muaj pab pawg los ntawm Oracle?
Taw qhia rau Oracle HAVING clause Nws yog siv los lim cov pab pawg ntawm cov kab rov qab los ntawm GROUP BY clause. Yog tias koj siv HAVING clause yam tsis muaj GROUP BY clause, HAVING clause ua haujlwm zoo li WHERE clause. Nco ntsoov tias HAVING clause lim cov pab pawg ntawm cov kab thaum lub WHERE clause lim kab