Video: Dab tsi yog qhov ntau tshaj ntawm cov rooj uas tuaj yeem koom nrog ib qho lus nug?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Cov ntau tshaj ntawm cov rooj uas tuaj yeem tau hais nyob rau hauv a ib leeg koom yog 61. Qhov no kuj siv tau rau lub tus naj npawb ntawm cov rooj uas tuaj yeem raug xa mus rau hauv lub ntsiab lus ntawm kev pom.
Ib yam li ntawd, tib neeg nug, peb puas tuaj yeem koom nrog ntau dua 2 lub rooj hauv SQL?
Koom nrog ntau dua ob rooj . Kev koom tes tsis txwv rau ob rooj . Koj tuaj yeem koom nrog ntau dua ob rooj hauv ib leeg SQL ntawv nqe lus.
Ib sab saum toj no, pes tsawg lub rooj tuaj yeem suav nrog hauv kev koom nrog? Kev piav qhia: Koom nrog tuaj yeem siv rau ntau tshaj ib rooj . Rau 'n' rooj qhov no koom cov xwm txheej xav tau yog 'n-1'.
Hais txog qhov no, pes tsawg lub rooj peb tuaj yeem koom nrog ib lub sijhawm hauv SQL?
Qhov siab tshaj plaws ntawm cov ntxhuav uas tuaj yeem koom nrog siv ib qho SELECT yog txwv rau 61. Qhov kev txwv tib yam muaj feem xyuam rau cov kev pom thiab. Rau SQL Server: Hauv versions dhau los ntawm SQL Server mus txog SQL Server 2005, qhov txwv kom koom nrog cov rooj siab tshaj plaws uas siv ib qho SELECT yog 256.
Kuv tuaj yeem koom nrog 3 lub rooj hauv SQL?
Yog tias koj xav tau cov ntaub ntawv los ntawm ntau yam rooj nyob rau hauv ib qho SELECT query koj yuav tsum tau siv ib qho subquery los yog Koom . Feem ntau peb tsuas yog lub sijhawm koom ob rooj zoo li Cov Neeg Ua Haujlwm thiab Lub Tsev Haujlwm tab sis qee zaum koj yuav xav tau koom ntau tshaj ob rooj thiab ib rooj plaub nrov yog koom peb tables hauv SQL.
Pom zoo:
Yuav ua li cas koj tuaj yeem txav qhov taw tes nrawm nrawm mus rau qhov pib ntawm cov lus nug cov lus nug?
T lossis F: Nias Ctrl + txoj cai xub yuam sij kom txav qhov taw tes rau qhov pib ntawm lo lus tom ntej
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