Video: Ib kab subquery yog dab tsi?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Ib Kab Subqueries . A ib kab subquery rov xoom lossis ib qho kab mus rau sab nrauv SQL nqe lus. Koj tuaj yeem tso ib subquery nyob rau hauv ib lub ntsiab lus nyob qhov twg, muaj cov kab lus, los yog FROM clause ntawm ib nqe lus SELECT.
Ua raws li qhov no hauv kev txiav txim siab, qhov txawv ntawm ib kab subquery thiab ntau kab subquery yog dab tsi?
Ib leeg - kab subqueries yog subqueries siv nrog a piv txwv hauv a THAUM, lossis HAVING clause. Subqueries uas tuaj yeem rov qab ntau dua ib qho kab (tab sis tsuas yog ib kem xwb) rau cov lus sab nrauv hu ua ntau - kab subqueries . Ntau - kab subqueries yog subqueries siv nrog ib IN , XAIV, los yog ALL clause.
Ib yam li ntawd, ntau kab subquery yog dab tsi? Ntau Kab Sub Query Ntau - kab subqueries yog cov lus nug nested uas tuaj yeem xa rov qab ntau dua ib qho kab ntawm cov txiaj ntsig rau niam txiv query. Ntau - kab subqueries feem ntau yog siv nyob rau hauv qhov twg thiab HAVING clauses. Txij li thaum nws rov qab los ntau kab , nws yuav tsum tau ua los ntawm cov neeg ua haujlwm sib piv (IN, ALL, ANY).
Raws li, leej twg yog ib kab subquery tswv?
Cov cov neeg ua haujlwm uas tuaj yeem siv nrog ib leeg - kab subqueires yog =, >, >=, <, <=, thiab. Pab pawg ua haujlwm tuaj yeem siv rau hauv subquery . Piv txwv li, nqe lus hauv qab no khaws cov ntsiab lus ntawm tus neeg ua haujlwm tuav cov nyiaj hli siab tshaj plaws. Muaj-clause kuj tuaj yeem siv nrog cov ib leeg - kab subquery.
Ib subquery puas tuaj yeem rov qab ntau kab?
Ntau Kab Subqueries Ntau kab subquery rov qab ib los yog ntau tshaj kab mus rau sab nrauv SQL ntawv nqe lus. Koj tuaj yeem siv IN, IB TUG, lossis TAG NRHO tus neeg teb xov tooj hauv cov lus nug sab nrauv los lis a subquery uas rov qab ntau kab . Cov ntsiab lus: Siv TSIS IN tus neeg teb xov tooj nrog a Ntau Kab Subquery.
Pom zoo:
Dab tsi yog qhov txawv ntawm tus kab mob los ntawm tus kab mob?
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