Dab tsi yog cov neeg ua haujlwm siv tau nyob rau hauv qhov twg clause?
Dab tsi yog cov neeg ua haujlwm siv tau nyob rau hauv qhov twg clause?

Video: Dab tsi yog cov neeg ua haujlwm siv tau nyob rau hauv qhov twg clause?

Video: Dab tsi yog cov neeg ua haujlwm siv tau nyob rau hauv qhov twg clause?
Video: Tshuaj theem vim li cas thiaj tau nqi ?/ Siv kho mob dab tsi?/paris polyphylla use for? 2024, Kaum ib hlis
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SQL WHERE clause yog siv los txwv cov kab uas cuam tshuam los ntawm SELECT, UPDATE lossis DELETE nug . Qhov WHERE clause tuaj yeem siv ua ke nrog logical operators xws li THIAB thiab OR, cov neeg ua haujlwm sib piv xws li, = etc. Thaum siv nrog AND logical tus neeg teb xov tooj , tag nrho cov txheej txheem yuav tsum tau ua.

Ua li no, tuaj yeem siv tau nyob rau qhov twg clause?

SQL Server muaj ntau yam ke muaj nuj nqi uas ua tau ua siv los yog hauv koj qhov SELECT lus los yog hauv koj qhov chaw lus.

Ib yam li ntawd, kev siv hauv thiab ntawm tus neeg teb xov tooj yog dab tsi? SQL | NTAU & IN Tus neeg ua haujlwm . Lub SQL NTAU xwm txheej tso cai rau koj sim yooj yim yog hais tias ib qho kev qhia nyob rau hauv ib tug ntau yam ntawm qhov tseem ceeb (inclusion). Cov nqi tuaj yeem yog cov ntawv nyeem, hnub tim, lossis tus lej. Nws tuaj yeem siv tau hauv SELECT, INSERT, UPDATE, lossis DELETE nqe lus.

Ib yam li ntawd, peb puas tuaj yeem siv muaj thiab nyob qhov twg clause ua ke?

A HNUB NO zoo ib yam li qhov chaw lus , tab sis tsuas yog siv rau cov pab pawg tag nrho (uas yog, rau cov kab hauv cov txiaj ntsig tau teeb tsa sawv cev rau pawg), qhov chaw nyob lus siv rau cov kab ib leeg. Ib qho lus nug ua tau muaj ob qho chaw nyob lus thiab a HNUB NTAWD . Cov HNUB NTAWD yog tom qab ntawd siv rau cov kab hauv qhov tshwm sim.

Peb puas tuaj yeem siv koom nrog tom qab qhov twg clause?

Hauv SQL, nws puas tuaj yeem ntxig a JOIN clause tom qab ib CHAW lus ? Tsis yog, nws tsis tau. Qhov kev txiav txim ntawm kev ua haujlwm yog ib txwm Koom thawj thiab qhov twg tom qab.

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