Video: SQL tsuas yog ua haujlwm li cas?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
SQL ntawv - TSEEM CEEB Clause. Cov SQL EXCEPT clause/operator yog siv los ua ke ob nqe lus SELECT thiab xa rov qab kab los ntawm thawj nqe lus SELECT uas tsis xa 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.
Ntawm no, dab tsi yog ib qho lus nug rov qab?
Cov TSEEM CEEB tus neeg teb xov tooj yog siv los tshem tawm xws li kab uas pom hauv ib qho nug tab sis tsis yog lwm tus. Nws rov qab los kab uas yog tshwj xeeb rau ib qho tshwm sim. Yuav siv lub TSEEM CEEB tus neeg teb xov tooj, ob qho tib si lus nug yuav tsum rov qab los tib tus naj npawb ntawm kab thiab cov kab yuav tsum yog cov ntaub ntawv sib xws.
Kuv yuav ua li cas xaiv txhua kab tshwj tsis yog ib qho hauv SQL? Tsuas yog nyem rau ntawm lub rooj> Script table as> Xaiv mus> New Query window. Koj yuav pom cov xaiv nug. Tsuas yog tshem tawm cov kem koj xav cais thiab koj muaj koj nyiam xaiv nug. Qhov no tsis yog ib qho kev daws teeb meem, tab sis qee cov ntaub ntawv tso cai rau koj siv cov kab lus tsis tu ncua los qhia qhov kab.
Ua kom pom qhov no, qhov txawv ntawm qhov rho tawm thiab tshwj tsis yog hauv SQL?
Tsis muaj kiag li qhov sib txawv hauv EXCEPT clause thiab MINUS lus. Lawv ob leeg ua haujlwm tib lub hom phiaj thiab lawv tsuas yog ob txoj hauv kev sib txawv ntawm kev ua tiav tib txoj haujlwm. Cov txawv yog tias TSEEM CEEB muaj hauv PostgreSQL database thaum MINUS muaj nyob rau hauv MySQL thiab Oracle.
Tsis muaj SQL?
Cov SQL tsis muaj Tus neeg teb xov tooj yuav ua qhov sib txawv rau EXISTS Tus neeg ua haujlwm. Nws yog siv los txwv tus naj npawb ntawm kab rov qab los ntawm SELECT Statement. Cov TSIS MUAJ hauv SQL ntawv Server yuav tshawb xyuas Subquery rau kab muaj nyob , thiab yog tsis muaj kab ces nws yuav rov TRUE, txwv tsis pub FALSE.
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