Video: Koj puas tuaj yeem siv pab pawg tsis muaj kev sib sau?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Koj siv tau tus PIB YOG clause tsis muaj thov ib tag nrho 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.
Tsuas yog li ntawd, peb puas tuaj yeem siv tag nrho cov haujlwm tsis muaj pab pawg los ntawm?
Yog lawm koj siv tau ib aggregate tsis muaj GROUP LOS NTAWM: SELECT SUM(col) NTAWM tbl; Koj tshem cov kab los ntawm SELECT sab hauv aggregate functions , tag nrho lwm cov kab yuav tsum muaj nyob rau hauv PIB BY clause cais los ntawm comma.
Kuj Paub, yog pab pawg los ntawm kev sib sau ua haujlwm? Cov PIB LOS NTAWM nqe lus pab pawg kab uas muaj cov txiaj ntsig zoo ib yam rau hauv cov kab lus, xws li "nrhiav tus naj npawb ntawm cov neeg siv khoom hauv txhua lub teb chaws". Cov PIB BY nqe lus feem ntau siv nrog aggregate functions (COUNT, MAX, MIN, SUM, AVG) rau pab pawg qhov tshwm sim-set los ntawm ib lossis ntau kab.
Ua ke, peb puas tuaj yeem siv pab pawg los ntawm yam tsis muaj kab lus?
Siv muaj tsis muaj pab pawg los ntawm. Cov lus nug nrog a muaj clause yuav tsum muaj ib pab pawg los ntawm lus . Yog koj omit pab pawg los ntawm, tag nrho cov kab tsis cais los ntawm qhov twg lus rov los ua ib leeg xwb 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.
Peb puas tuaj yeem siv pab pawg los ntawm kev koom nrog?
Koj ua tau nug cov ntaub ntawv los ntawm ntau lub rooj siv INNER Koom clause, tiam siv tus PIB BY clause rau pab pawg kab mus rau hauv ib txheej ntawm cov kab lus xaus.
Pom zoo:
Cov pivot puas tuaj yeem siv yam tsis muaj kev sib sau ua ke?
Koj tsis tuaj yeem tshem tawm cov haujlwm sib sau ua ke, tab sis koj tuaj yeem tsim koj cov lus nug raws li koj xav tau. Static PIVOT query
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
Peb puas tuaj yeem hloov cov pab pawg hauv zos rau pab pawg thoob ntiaj teb?
Domain cov pab pawg hauv zos mus rau universal pawg: Cov pab pawg hauv zos uas tau hloov dua siab tshiab tsis tuaj yeem muaj lwm pab pawg hauv zos. Universal pab pawg mus rau ntiaj teb no los yog domain pab pawg neeg hauv zos: Rau kev hloov dua siab tshiab rau ntiaj teb no pab pawg, universal pawg hloov dua siab tshiab tsis tuaj yeem muaj cov neeg siv lossis pab pawg thoob ntiaj teb los ntawm lwm tus sau
Pab pawg tuaj yeem siv yam tsis muaj?
Siv tsis muaj pab pawg los ntawm. Ib qho lus nug uas muaj kab lus yuav tsum muaj ib pawg los ntawm kab lus. Yog tias koj tshem tawm pawg los ntawm, tag nrho cov kab tsis suav nrog qhov twg clause rov qab los ua ib pab pawg. Vim tias tsis muaj kev sib koom ua ke ntawm qhov chaw thiab muaj cov kab lus, lawv tsis tuaj yeem ua lawv tus kheej ntawm ib leeg
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