Yog tias koj nyuam qhuav pib nrog cov ntaub ntawv, qhov kev sau ntawm cov khoom saum toj kawg nkaus uas koj yuav tsum paub yuav pab koj mus tom ntej. Cov lus tseeb no tau lees paub los ua kom yooj yim rau kev ua haujlwm nrog cov ntaub ntawv thiab ua kom cov khoom tsim tau.
SQL Forms cov tub ntxhais ntawm Relational Databases
Cov Lus Nug Cov Lus Nug (SQL) tsim lub hauv paus ntawm txhua qhov kev sib raug zoo databases. Nws muab ib qho kev sib cuam tshuam rau Oracle, SQL Server, Microsoft Access, thiab lwm cov ntaub ntawv sib raug zoo thiab yog "yuav tsum kawm" rau txhua tus neeg siv cov ntaub ntawv xav tau.
Ua ib qho kev qhia SQL ua ntej koj sim kawm ib qho software database tshwj xeeb. Lub sij hawm nqis peev yuav pab koj tsim lub hauv paus tsim nyog thiab pib ntawm qhov tseeb ko taw hauv ntiaj teb ntawm cov ntaub ntawv.
W3Schools.com yog qhov chaw pib zoo rau cov neeg pib nyiam SQL.
Xaiv cov yuam sij tseem ceeb yog qhov kev txiav txim siab tseem ceeb
Kev xaiv tus yuam sij tseem ceeb yog ib qho kev txiav txim siab tseem ceeb tshaj plaws uas koj yuav ua thaum tsim cov ntaub ntawv tshiab. Qhov kev txwv tseem ceeb tshaj plaws yog koj yuav tsum xyuas kom meej tias tus yuam sij xaiv yog qhov tshwj xeeb.
Yog tias tus cwj pwm muaj txiaj ntsig yuav nyob hauv ob cov ntaub ntawv, tus cwj pwm sib koom yog qhov kev xaiv tsis zoo rau tus yuam sij tseem ceeb. Tej zaum koj yuav tsum tsis txhob muaj qhov tseem ceeb uas ua rau muaj kev txhawj xeeb txog kev ceev ntiag tug, xws li tus lej Xaus Saus.
NULL Tsis Zero lossis Kab Ntsig
NULL yog tus nqi tshwj xeeb hauv ntiaj teb ntawm cov ntaub ntawv, tab sis nws yog ib yam uas feem ntau cuam tshuam rau cov pib tshiab.
Thaum koj pom tus nqi NULL, txhais nws li "tsis paub." Piv txwv li, yog tias qhov ntau yog NULL, qhov ntawd tsis tas txhais tau tias nws yog xoom. Ib yam li ntawd, yog tias daim ntawv teb tuav tus nqi NULL, nws tsis txhais hais tias tsis muaj tus nqi tsim nyog - nws tsuas yog tsis paub.
Xav txog cov ntaub ntawv uas muaj cov ntaub ntawv hais txog cov menyuam yaus uas mus kawm ib lub tsev kawm ntawv tshwj xeeb. Yog tias tus neeg nkag mus rau hauv cov ntaub ntawv tsis paub tus tub ntxhais kawm lub hnub nyoog, tus nqi NULL yog siv los qhia qhov "tsis paub" qhov chaw. Tus menyuam kawm ntawv yeej muaj hnub nyoog; nws tsuas yog tsis nyob hauv database.
Kev Hloov Cov Ntawv Qhia rau Cov Ntaub Ntawv Txuag Sijhawm
Yog tias koj muaj tons ntawm cov ntaub ntawv khaws cia hauv Microsoft Excel lossis lwm hom ntawv nthuav dav, koj tuaj yeem txuag koj tus kheej lub sijhawm los ntawm kev hloov cov ntawv nthuav tawm mus rau hauv cov ntaub ntawv database.
Txhua Database Platforms Tsis Tsim Nyog
Muaj ntau cov ntaub ntawv tawm muaj, thiab txhua tus muaj cov yam ntxwv tshwj xeeb ntawm cov nqi sib txawv.
Qee yog cov tuam txhab lag luam uas muaj cov ntaub ntawv tsim nyog tsim los tuav cov ntaub ntawv loj loj rau cov lag luam thoob ntiaj teb. Lwm tus yog desktop databases zoo dua rau kev taug qab cov khoom muag rau lub khw me me nrog ib lossis ob tus neeg siv.
Koj cov kev xav tau ntawm kev lag luam yuav sau cov ntaub ntawv tsim nyog rau koj cov kev xav tau, thiab muaj ntau tus neeg tsim cov ntaub ntawv dawb online xaiv los ntawm.
