Video: Kuv tuaj yeem siv tsis zoo li hauv SQL?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Cov TSIS ZOO tus neeg ua haujlwm hauv SQL ntawv yog siv ntawm ib kab uas yog hom varchar. Feem ntau, nws yog siv nrog % uas yog siv los sawv cev rau txhua txoj hlua tus nqi, suav nrog tus cim null. Txoj hlua peb hla mus rau tus neeg teb xov tooj no yog tsis yog case-sensitive.
Hais txog qhov no, siv dab tsi hauv SQL?
Cov SQL ntawv Nyob rau hauv qhov xwm txheej (qee zaus hu ua IN tus neeg teb xov tooj) tso cai rau koj los sim yooj yim yog tias qhov kev qhia cuam tshuam ib qho nqi hauv cov npe ntawm cov txiaj ntsig. Nws yog siv los pab txo qhov kev xav tau ntau yam LOSSIS nyob rau hauv SELECT, INSERT, UPDATE, lossis DELETE nqe lus.
Ib yam li ntawd, tsuas yog tus neeg teb xov tooj hauv SQL yog dab tsi? Cov SQL EXCEPT kab lus/ tus neeg ua haujlwm yog siv los ua ke ob nqe lus SELECT thiab xa rov qab kab los ntawm thawj nqe lus SELECT uas tsis rov qab los ntawm daim ntawv thib ob SELECT. Qhov no txhais tau tias TSEEM CEEB rov qab tsuas yog kab, uas tsis muaj nyob rau hauv nqe lus SELECT thib ob.
Kuj paub yog, kuv yuav tshem tawm cov ntaub ntawv hauv SQL li cas?
EXCEPT tus neeg teb xov tooj yog siv rau cais tawm nyiam kab uas pom nyob rau hauv ib qho lus nug tab sis tsis yog lwm qhov. Nws rov qab los kab uas yog qhov tshwj xeeb rau ib qho txiaj ntsig. Txhawm rau siv EXCEPT tus neeg teb xov tooj, ob qho lus nug yuav tsum xa rov qab tib tus lej ntawm kab thiab cov kab yuav tsum sib haum cov ntaub ntawv hom.
Dab tsi tsis zoo li hauv SQL?
MySQL TSIS ZOO yog siv los tshem tawm cov kab uas phim cov txheej txheem ua raws li LIKE tus neeg ua haujlwm. Txawv sib piv siv SQL ntawv yooj yim tsis tu ncua qhia piv. Rov qab 1 (TRUE) lossis 0 (FALSE). Yog tias expr lossis pat yog NULL, qhov tshwm sim yog NULL.
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